Add comprehensive telemetry enhancements for better product insights:

Runtime & Platform Data:
- Add runtimeType (local/worktree/ssh) to workspace_created and message_sent
- Add frontend platform info (userAgent, platform) for mux server mode
- Enhance backend platform data with nodeVersion and bunVersion

New Events:
- stream_completed: Track completion vs interruption, duration, output tokens
- provider_configured: Track which providers users set up (not keys!)
- command_used: Track slash command usage patterns
- voice_transcription: Track voice input adoption and success rate

Enhanced Events:
- app_started: Add vimModeEnabled for vim mode adoption
- message_sent: Add thinkingLevel for extended thinking usage

All metrics use base-2 rounding for privacy-preserving numerical data.

_Generated with `mux`_

Move rounding logic into centralized tracking functions so callers
don't need to manually call roundToBase2(). This ensures consistent
privacy-preserving transformations across all telemetry call sites.

Changes:
- Add src/common/telemetry/tracking.ts with all tracking functions
- Tracking functions accept raw values and handle rounding internally
- Remove roundToBase2/getFrontendPlatformInfo from public exports
- Simplify useTelemetry hook to delegate to tracking functions
- Update WorkspaceStore, useVoiceInput, chatCommands to use new API

The public API is now cleaner:
- trackMessageSent(model, mode, messageLength, ...) - no rounding needed
- trackStreamCompleted(model, interrupted, durationSecs, outputTokens)
- trackVoiceTranscription(audioDurationSecs, success)

_Generated with `mux`_