Implement hybrid print preview with CSS-based approach

- Add hidden print-preview-copy div at app level for clean print isolation
- Use @media print rules to show only print copy (960x720) in landscape
- Auto-sync print copy with preview content on modal render via use_effect
- Copy CSS variables and data attributes for proper hour filtering
- Set explicit dimensions matching print-preview-paper content area
- Force landscape orientation with @page rule for better calendar printing

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

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

frontend/Cargo.toml

@@ -30,6 +30,8 @@ web-sys = { version = "0.3", features = [
     "RequestMode",
     "Response",
     "CssStyleDeclaration",
+    "MediaQueryList",
+    "MediaQueryListEvent",
 ] }
 wasm-bindgen = "0.2"
 js-sys = "0.3"