Implement lightweight auth system with SQLite

Added SQLite database for session management and user preferences storage,
allowing users to have consistent settings across different sessions and devices.

Backend changes:
- Added SQLite database with users, sessions, and preferences tables
- Implemented session-based authentication alongside JWT tokens
- Created preference storage/retrieval API endpoints
- Database migrations for schema setup
- Session validation and cleanup functionality

Frontend changes:
- Added "Remember server" and "Remember username" checkboxes to login
- Created preferences service for syncing settings with backend
- Updated auth flow to handle session tokens and preferences
- Store remembered values in LocalStorage (not database) for convenience

Key features:
- User preferences persist across sessions and devices
- CalDAV passwords never stored, only passed through
- Sessions expire after 24 hours
- Remember checkboxes only affect local browser storage

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/src/components/login.rs

@@ -9,11 +9,24 @@ pub struct LoginProps {
 
 #[function_component]
 pub fn Login(props: &LoginProps) -> Html {
-    let server_url = use_state(String::new);
-    let username = use_state(String::new);
+    // Load remembered values from LocalStorage on mount
+    let server_url = use_state(|| {
+        LocalStorage::get::<String>("remembered_server_url").unwrap_or_default()
+    });
+    let username = use_state(|| {
+        LocalStorage::get::<String>("remembered_username").unwrap_or_default()
+    });
     let password = use_state(String::new);
     let error_message = use_state(|| Option::<String>::None);
     let is_loading = use_state(|| false);
+    
+    // Remember checkboxes state
+    let remember_server = use_state(|| {
+        LocalStorage::get::<String>("remembered_server_url").is_ok()
+    });
+    let remember_username = use_state(|| {
+        LocalStorage::get::<String>("remembered_username").is_ok()
+    });
 
     let server_url_ref = use_node_ref();
     let username_ref = use_node_ref();
@@ -42,6 +55,38 @@ pub fn Login(props: &LoginProps) -> Html {
             password.set(target.value());
         })
     };
+    
+    let on_remember_server_change = {
+        let remember_server = remember_server.clone();
+        let server_url = server_url.clone();
+        Callback::from(move |e: Event| {
+            let target = e.target_unchecked_into::<HtmlInputElement>();
+            let checked = target.checked();
+            remember_server.set(checked);
+            
+            if checked {
+                let _ = LocalStorage::set("remembered_server_url", (*server_url).clone());
+            } else {
+                let _ = LocalStorage::delete("remembered_server_url");
+            }
+        })
+    };
+    
+    let on_remember_username_change = {
+        let remember_username = remember_username.clone();
+        let username = username.clone();
+        Callback::from(move |e: Event| {
+            let target = e.target_unchecked_into::<HtmlInputElement>();
+            let checked = target.checked();
+            remember_username.set(checked);
+            
+            if checked {
+                let _ = LocalStorage::set("remembered_username", (*username).clone());
+            } else {
+                let _ = LocalStorage::delete("remembered_username");
+            }
+        })
+    };
 
     let on_submit = {
         let server_url = server_url.clone();
@@ -73,7 +118,7 @@ pub fn Login(props: &LoginProps) -> Html {
             wasm_bindgen_futures::spawn_local(async move {
                 web_sys::console::log_1(&"🚀 Starting login process...".into());
                 match perform_login(server_url.clone(), username.clone(), password.clone()).await {
-                    Ok((token, credentials)) => {
+                    Ok((token, session_token, credentials, preferences)) => {
                         web_sys::console::log_1(&"✅ Login successful!".into());
                         // Store token and credentials in local storage
                         if let Err(_) = LocalStorage::set("auth_token", &token) {
@@ -82,11 +127,22 @@ pub fn Login(props: &LoginProps) -> Html {
                             is_loading.set(false);
                             return;
                         }
+                        if let Err(_) = LocalStorage::set("session_token", &session_token) {
+                            error_message
+                                .set(Some("Failed to store session token".to_string()));
+                            is_loading.set(false);
+                            return;
+                        }
                         if let Err(_) = LocalStorage::set("caldav_credentials", &credentials) {
                             error_message.set(Some("Failed to store credentials".to_string()));
                             is_loading.set(false);
                             return;
                         }
+                        
+                        // Store preferences from database
+                        if let Ok(prefs_json) = serde_json::to_string(&preferences) {
+                            let _ = LocalStorage::set("user_preferences", &prefs_json);
+                        }
 
                         is_loading.set(false);
                         on_login.emit(token);
@@ -117,6 +173,15 @@ pub fn Login(props: &LoginProps) -> Html {
                             onchange={on_server_url_change}
                             disabled={*is_loading}
                         />
+                        <div class="remember-checkbox">
+                            <input
+                                type="checkbox"
+                                id="remember_server"
+                                checked={*remember_server}
+                                onchange={on_remember_server_change}
+                            />
+                            <label for="remember_server">{"Remember server"}</label>
+                        </div>
                     </div>
 
                     <div class="form-group">
@@ -130,6 +195,15 @@ pub fn Login(props: &LoginProps) -> Html {
                             onchange={on_username_change}
                             disabled={*is_loading}
                         />
+                        <div class="remember-checkbox">
+                            <input
+                                type="checkbox"
+                                id="remember_username"
+                                checked={*remember_username}
+                                onchange={on_remember_username_change}
+                            />
+                            <label for="remember_username">{"Remember username"}</label>
+                        </div>
                     </div>
 
                     <div class="form-group">
@@ -177,7 +251,7 @@ async fn perform_login(
     server_url: String,
     username: String,
     password: String,
-) -> Result<(String, String), String> {
+) -> Result<(String, String, String, serde_json::Value), String> {
     use crate::auth::{AuthService, CalDAVLoginRequest};
     use serde_json;
 
@@ -201,7 +275,17 @@ async fn perform_login(
                 "username": username,
                 "password": password
             });
-            Ok((response.token, credentials.to_string()))
+            
+            // Extract preferences as JSON
+            let preferences = serde_json::json!({
+                "calendar_selected_date": response.preferences.calendar_selected_date,
+                "calendar_time_increment": response.preferences.calendar_time_increment,
+                "calendar_view_mode": response.preferences.calendar_view_mode,
+                "calendar_theme": response.preferences.calendar_theme,
+                "calendar_colors": response.preferences.calendar_colors,
+            });
+            
+            Ok((response.token, response.session_token, credentials.to_string(), preferences))
         }
         Err(err) => {
             web_sys::console::log_1(&format!("❌ Backend error: {}", err).into());