feat: optimize reaction message format to reduce airtime

- Reduce reaction payload from ~44 bytes to 9 bytes (5x smaller)
- Use 4-char hex hash (timestamp + sender + first 5 chars) for message ID
- Use 2-char hex emoji index instead of multi-byte UTF-8 emoji
- Format: r:HASH:INDEX (e.g., r:a1b2:00)
- For 1:1 chats, sender is implicit (null) for shorter hash
- Prevent users from reacting to their own messages
- Add room server reaction support with sender identification
- Make emoji lists public in EmojiPicker for shared indexing
- Add 💪 and 🚀 emojis to picker
- Add comprehensive unit tests for reaction helpers
- Update minor dependencies

macos/Flutter/GeneratedPluginRegistrant.swift

@@ -9,7 +9,6 @@ import flutter_blue_plus_darwin
 import flutter_local_notifications
 import mobile_scanner
 import package_info_plus
-import path_provider_foundation
 import shared_preferences_foundation
 import sqflite_darwin
 import url_launcher_macos
@@ -20,7 +19,6 @@ func RegisterGeneratedPlugins(registry: FlutterPluginRegistry) {
   FlutterLocalNotificationsPlugin.register(with: registry.registrar(forPlugin: "FlutterLocalNotificationsPlugin"))
   MobileScannerPlugin.register(with: registry.registrar(forPlugin: "MobileScannerPlugin"))
   FPPPackageInfoPlusPlugin.register(with: registry.registrar(forPlugin: "FPPPackageInfoPlusPlugin"))
-  PathProviderPlugin.register(with: registry.registrar(forPlugin: "PathProviderPlugin"))
   SharedPreferencesPlugin.register(with: registry.registrar(forPlugin: "SharedPreferencesPlugin"))
   SqflitePlugin.register(with: registry.registrar(forPlugin: "SqflitePlugin"))
   UrlLauncherPlugin.register(with: registry.registrar(forPlugin: "UrlLauncherPlugin"))