feat(overlay): add multi-instance chat overlay

[Drilmo]

Summary

Add a new customizable chat overlay that can display messages and events from Twitch, YouTube, TikTok and Kick streams.

Features

• Multiple overlay instances with independent configurations
• 7 visual styles: default, twitch, bubbles, gradient, neon, minimal, glass (liquid glass effect)
• All event types supported: follows, subs, raids, cheers, bans, rewards, donations (Ko-fi, Streamlabs, StreamElements, Tipeee, Tiltify, Patreon), etc.
• Multi-channel support: source indicator when connected to multiple channels, connect/disconnect messages with channel avatar
• Configurable: message duration, delay, max messages, entrance animations (6 types), size presets (6 sizes)
• Filters: by platform, message type, users, and commands
• Full i18n support (EN/FR) for all event labels
• CSS customization documentation for streamers

Files changed

• OverlayChat.vue: Main overlay component
• OverlayParamsChat.vue: Configuration panel
• storeChat.ts: Data persistence and event handling
• TwitchatDataTypes.ts: ChatOverlayParams and ChatOverlayLabels types
• i18n/en/overlay.json & i18n/fr/overlay.json: Translations

Test plan

• [ ] Create a new chat overlay instance
• [ ] Test each visual style (default, twitch, bubbles, gradient, neon, minimal, glass)
• [ ] Verify messages and events display correctly
• [ ] Test filters (platform, message types, users)
• [ ] Test entrance animations
• [ ] Verify i18n works in both EN and FR
• [ ] Test multi-channel source indicator
• [ ] Verify CSS customization works via OBS browser source

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