#21005: feat(tts): add path delivery mode to prevent duplicate sends

## Summary - add optional `delivery` parameter to the `tts` tool: - `auto` (default): existing behavior, emits `MEDIA:` for automatic delivery - `path`: returns `AUDIO_PATH:` for manual `message.send` workflows - update tool guidance text to make duplicate-send avoidance explicit - add unit tests for default auto mode and new path mode ## Why When callers need manual control (for example, custom Telegram voice-note pipelines), returning a plain path avoids accidental duplicate audio sends while preserving backward compatibility. ## Validation - `pnpm vitest run --config vitest.unit.config.ts src/agents/tools/tts-tool.test.ts`