feat: add close confirmation modal with minimize to tray option

Implemented a confirmation modal when users try to close the application:
- Modal always shows with three options: Cancel, Minimize to Tray, Close Application
- Detects if Claude is actively running and shows appropriate warning message
- Removed minimize_to_tray config setting (no longer needed)
- Added core:window:allow-hide permission for window hiding
- Created CloseAppConfirmModal component with keyboard shortcuts (Escape to cancel)
- Added close_application command to properly exit the app
- Backend emits window-close-requested event for frontend to handle

This provides better UX by giving users clear choices every time they close,
preventing accidental closures during active work sessions.

src-tauri/src/config.rs

@@ -71,9 +71,6 @@ pub struct HikariConfig {
     #[serde(default = "default_font_size")]
     pub font_size: u32,
 
-    #[serde(default)]
-    pub minimize_to_tray: bool,
-
     #[serde(default)]
     pub streamer_mode: bool,
 
@@ -134,7 +131,6 @@ impl Default for HikariConfig {
             update_checks_enabled: true,
             character_panel_width: None,
             font_size: 14,
-            minimize_to_tray: false,
             streamer_mode: false,
             streamer_hide_paths: false,
             compact_mode: false,
@@ -242,7 +238,6 @@ mod tests {
         assert!(config.update_checks_enabled);
         assert!(config.character_panel_width.is_none());
         assert_eq!(config.font_size, 14);
-        assert!(!config.minimize_to_tray);
         assert!(!config.streamer_mode);
         assert!(!config.streamer_hide_paths);
         assert!(!config.compact_mode);
@@ -275,7 +270,6 @@ mod tests {
             update_checks_enabled: true,
             character_panel_width: Some(400),
             font_size: 16,
-            minimize_to_tray: true,
             streamer_mode: false,
             streamer_hide_paths: false,
             compact_mode: false,