feat: comprehensive keyboard shortcuts for roundtable (T/V/Esc/Space/M/S/C)

[YizukiAme]

Summary

Adds comprehensive keyboard shortcuts for the roundtable to improve interaction speed, especially during live discussions where clicking small UI elements is inconvenient.

Closes #255

Shortcuts

Core (roundtable/index.tsx)

Key	Action	Guard
T	Toggle text input box	Disabled when typing in input/textarea
V	Toggle voice input	Disabled when typing; gated on asrEnabled; busyRef prevents rapid-fire
Escape	Dismiss open input/voice panels	Works even when input is focused; Keyboard Lock prevents fullscreen exit

Stage-level (stage.tsx)

Key	Action	Guard
Space	Play/pause lecture	Extended to work outside presentation mode
Escape	Exit fullscreen	Only when no panels are open
M	Toggle TTS mute	All modes
S	Toggle sidebar	Non-fullscreen only
C	Toggle chat panel	Non-fullscreen only

Changes

components/roundtable/index.tsx

• Extended existing Space-only keydown handler into unified shortcut handler
• Added T → handleToggleInput(), V → handleToggleVoice()
• Escape handled separately (before input guard) so it works while typing
• Moved useEffect after useAudioRecorder / handleToggleVoice declarations

components/stage.tsx

• Space for lecture play/pause now works outside presentation mode
• Escape handling: Keyboard Lock API (navigator.keyboard.lock(['Escape'])) prevents browser from auto-exiting fullscreen; our handler decides: panels open → roundtable closes them, no panels → exit fullscreen
• Added M/S/C shortcuts with appropriate fullscreen guards

lib/hooks/use-audio-recorder.ts

• Added busyRef synchronous lock to prevent rapid V press from creating duplicate SpeechRecognition instances
• Silenced non-fatal aborted error in onerror handler

Testing

• T → opens text input. T again → closes. Typing in input: T types normally
• V → starts voice recording. V again → stops. Rapid V press: no error
• Escape → closes any open panel (works from within text input too)
• Escape in fullscreen with panels open → closes panels only (no fullscreen exit)
• Escape in fullscreen with no panels → exits fullscreen
• Space → play/pause lecture from normal view (not just presentation)
• M → toggles TTS mute
• S → toggles sidebar (non-fullscreen)
• C → toggles chat panel (non-fullscreen)

🤖 AI-assisted and reviewed by Claude Opus 4.6

[YizukiAme]

Small addition not reflected in the description:

• Added ArrowUp / ArrowDown shortcuts for volume control

Will update the PR description if needed.

[wyuc]

Tested locally. Approved