Add AI voice control for the board

[brahim-guaali]

Summary

• AI voice control via floating mic button — users speak natural language commands to control the board (select cards, create streams, change status, search, focus, etc.)
• Persistent voice session — mic stays active across commands until the user taps to stop. After each TTS confirmation, recognition automatically restarts for the next command.
• Conversation context — Gemini chat history is maintained across turns so users can say "mark it as done" after "select the auth card" without re-specifying which card.
• Uses Gemini 2.5 Flash (already integrated via Firebase AI) with structured JSON output and Web Speech API (SpeechRecognition + SpeechSynthesis) — no new dependencies.

New files

File	Purpose
src/types/speech-recognition.d.ts	TypeScript declarations for the Web Speech API
src/hooks/useVoiceControl.ts	Core hook: state machine, speech recognition, Gemini command parsing, dispatch, TTS
src/components/voice/VoiceControlButton.tsx	Floating mic button with visual states (idle/listening/processing/speaking/error)
src/components/voice/VoiceToast.tsx	Transient toast for AI confirmations and errors

Modified files

File	Change
src/pages/ProjectPage.tsx	Integrates useVoiceControl hook, mounts VoiceControlButton in canvas (gated by !isReadOnly)
src/hooks/index.ts	Exports useVoiceControl
src/index.css	Adds fadeIn / slideUp keyframe animations

Supported voice commands

select_stream, create_stream, branch_stream, update_status, update_title, update_description, set_due_date, add_dependency, remove_dependency, add_note, delete_stream, search, focus_stream, unfocus, reset_view

Test plan

• Chrome: mic button visible, tap starts session (red pulse), speak "select [card name]" → card selected, sidebar opens, TTS confirms, mic resumes listening
• "Create a task called Sprint Planning" → new card appears on canvas
• "Mark [card] as done" → status changes, confetti fires
• Multi-turn: "Select auth card" → "Mark it as done" → resolves "it" from context
• "Search for auth" → search bar populates
• "Focus on [card]" → focus mode; "Exit focus" → returns
• "Zoom to fit" → canvas recenters
• Gibberish → AI returns error toast, session resumes listening
• Tap mic during processing/speaking → kills session immediately
• Read-only board: mic button not shown
• Unsupported browser (Firefox): mic button hidden

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