Add internationalization (i18n) support with English and Russian locales

- Add translation JSON files (en.json, ru.json) with 110+ strings each
- Implement locale auto-detection from browser settings
- Add locale toggle button (EN/RU) with localStorage persistence
- Translate all user-facing text: auth, player, scripts, callbacks
- Fix dynamic content translation on locale switch (playback state, track title)
- Add comprehensive i18n documentation to CLAUDE.md
- Follow existing theme toggle pattern for consistency

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

media_server/static/locales/en.json

@@ -0,0 +1,109 @@
+{
+  "app.title": "Media Server",
+  "auth.message": "Enter your API token to connect to the media server.",
+  "auth.placeholder": "Enter API Token",
+  "auth.connect": "Connect",
+  "auth.help": "To get your token, run:",
+  "auth.logout": "Logout",
+  "auth.logout.title": "Clear saved token",
+  "auth.invalid": "Invalid token. Please try again.",
+  "auth.cleared": "Token cleared. Please enter a new token.",
+  "auth.required": "Please enter a token",
+  "player.theme": "Toggle theme",
+  "player.locale": "Change language",
+  "player.previous": "Previous",
+  "player.play": "Play/Pause",
+  "player.next": "Next",
+  "player.mute": "Mute",
+  "player.status.connected": "Connected",
+  "player.status.disconnected": "Disconnected",
+  "player.no_media": "No media playing",
+  "player.source": "Source:",
+  "player.unknown_source": "Unknown",
+  "state.playing": "Playing",
+  "state.paused": "Paused",
+  "state.stopped": "Stopped",
+  "state.idle": "Idle",
+  "scripts.quick_actions": "Quick Actions",
+  "scripts.no_scripts": "No scripts configured",
+  "scripts.management": "Script Management",
+  "scripts.add": "Add",
+  "scripts.table.name": "Name",
+  "scripts.table.label": "Label",
+  "scripts.table.command": "Command",
+  "scripts.table.timeout": "Timeout",
+  "scripts.table.actions": "Actions",
+  "scripts.empty": "No scripts configured. Click 'Add' to create one.",
+  "scripts.dialog.add": "Add Script",
+  "scripts.dialog.edit": "Edit Script",
+  "scripts.field.name": "Script Name *",
+  "scripts.field.label": "Label",
+  "scripts.field.command": "Command *",
+  "scripts.field.description": "Description",
+  "scripts.field.icon": "Icon (MDI)",
+  "scripts.field.timeout": "Timeout (seconds)",
+  "scripts.placeholder.name": "Only letters, numbers, and underscores allowed",
+  "scripts.placeholder.label": "Human-readable name",
+  "scripts.placeholder.command": "e.g., shutdown /s /t 0",
+  "scripts.placeholder.description": "What does this script do?",
+  "scripts.placeholder.icon": "e.g., mdi:power",
+  "scripts.button.cancel": "Cancel",
+  "scripts.button.save": "Save",
+  "scripts.button.edit": "Edit",
+  "scripts.button.delete": "Delete",
+  "scripts.msg.executed": "{name} executed successfully",
+  "scripts.msg.execute_failed": "Failed to execute {name}",
+  "scripts.msg.execute_error": "Error executing {name}",
+  "scripts.msg.created": "Script created successfully",
+  "scripts.msg.updated": "Script updated successfully",
+  "scripts.msg.create_failed": "Failed to create script",
+  "scripts.msg.update_failed": "Failed to update script",
+  "scripts.msg.deleted": "Script deleted successfully",
+  "scripts.msg.delete_failed": "Failed to delete script",
+  "scripts.msg.not_found": "Script not found",
+  "scripts.msg.load_failed": "Failed to load script details",
+  "scripts.msg.list_failed": "Failed to load scripts",
+  "scripts.confirm.delete": "Are you sure you want to delete the script \"{name}\"?",
+  "callbacks.management": "Callback Management",
+  "callbacks.description": "Callbacks are scripts triggered automatically by media control events (play, pause, stop, etc.)",
+  "callbacks.add": "Add",
+  "callbacks.table.event": "Event",
+  "callbacks.table.command": "Command",
+  "callbacks.table.timeout": "Timeout",
+  "callbacks.table.actions": "Actions",
+  "callbacks.empty": "No callbacks configured. Click 'Add' to create one.",
+  "callbacks.dialog.add": "Add Callback",
+  "callbacks.dialog.edit": "Edit Callback",
+  "callbacks.field.event": "Event *",
+  "callbacks.field.command": "Command *",
+  "callbacks.field.timeout": "Timeout (seconds)",
+  "callbacks.field.workdir": "Working Directory",
+  "callbacks.placeholder.event": "Select event...",
+  "callbacks.placeholder.command": "e.g., shutdown /s /t 0",
+  "callbacks.placeholder.workdir": "Optional",
+  "callbacks.button.cancel": "Cancel",
+  "callbacks.button.save": "Save",
+  "callbacks.button.edit": "Edit",
+  "callbacks.button.delete": "Delete",
+  "callbacks.event.on_play": "on_play - After play succeeds",
+  "callbacks.event.on_pause": "on_pause - After pause succeeds",
+  "callbacks.event.on_stop": "on_stop - After stop succeeds",
+  "callbacks.event.on_next": "on_next - After next track succeeds",
+  "callbacks.event.on_previous": "on_previous - After previous track succeeds",
+  "callbacks.event.on_volume": "on_volume - After volume change",
+  "callbacks.event.on_mute": "on_mute - After mute toggle",
+  "callbacks.event.on_seek": "on_seek - After seek succeeds",
+  "callbacks.event.on_turn_on": "on_turn_on - Callback-only action",
+  "callbacks.event.on_turn_off": "on_turn_off - Callback-only action",
+  "callbacks.event.on_toggle": "on_toggle - Callback-only action",
+  "callbacks.msg.created": "Callback created successfully",
+  "callbacks.msg.updated": "Callback updated successfully",
+  "callbacks.msg.create_failed": "Failed to create callback",
+  "callbacks.msg.update_failed": "Failed to update callback",
+  "callbacks.msg.deleted": "Callback deleted successfully",
+  "callbacks.msg.delete_failed": "Failed to delete callback",
+  "callbacks.msg.not_found": "Callback not found",
+  "callbacks.msg.load_failed": "Failed to load callback details",
+  "callbacks.msg.list_failed": "Failed to load callbacks",
+  "callbacks.confirm.delete": "Are you sure you want to delete the callback \"{name}\"?"
+}