[Critical] AGENTS.md contains incorrect feature flag descriptions

[Coldaine]

Summary

AGENTS.md documentation contains incorrect feature flag descriptions that do not match the actual implementation.

Impact

• Developers will configure incorrect feature flags
• Build failures from non-existent flags
• Confusion about available STT backends

Current State

Actual implemented plugins (per mod.rs):

• parakeet - NVIDIA GPU plugin (production)
• moonshine - CPU plugin via PyO3
• mock - Testing
• noop - Null plugin

Recommended Fix

1. Update AGENTS.md to reflect actual feature flags
2. Remove references to vosk, whisper, coqui, leopard, silero
3. Document parakeet and moonshine configuration

Related

• Agent 8 (Documentation) review finding
• PR chore(stt): remove stub STT plugin files #282 removes Vosk references but AGENTS.md needs update

Priority

P0 - Fix this week (documentation)}