Rebrand application from 'Calendar App' to 'Runway'

- Update project name in Cargo.toml from calendar-app to runway
- Change HTML title and sidebar header to 'Runway'
- Complete README rewrite with new branding and philosophy
- Add 'The Name' section explaining runway metaphor as passive infrastructure
- Update Dockerfile build references to use new binary name
- Maintain all technical documentation with new branding context

The name 'Runway' embodies passive infrastructure that enables coordination
without getting in the way - like airport runways that provide essential
structure for planes but stay invisible during flight.

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

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

frontend/src/components/sidebar.rs

@@ -158,7 +158,7 @@ pub fn sidebar(props: &SidebarProps) -> Html {
     html! {
         <aside class="app-sidebar">
             <div class="sidebar-header">
-                <h1>{"Calendar App"}</h1>
+                <h1>{"Runway"}</h1>
                 {
                     if let Some(ref info) = props.user_info {
                         html! {