Adds dedicated renderer classes per channel type:
- MeshRenderer produces 1+ chunks <=200 chars with (k/N) counters
when the payload overflows. Reuses the toggle-label vocabulary
from the digest. Mesh channels skip re-chunking when the payload
already carries chunk_index metadata (digest path).
- EmailRenderer produces {subject, body} with structured context
lines. Plain text only; HTML body is a future polish.
- WebhookRenderer produces a JSON-serializable dict with stable
schema_version 1.0. Optional fields omitted (not nulled) for
compactness. Designed for reuse by Phase 2.6.5's MQTT event
publisher.
- All four channel implementations (MeshBroadcast, MeshDM, Email,
Webhook) now call their renderer in deliver() before transport.
- New renderer tests cover each renderer in isolation; new channel
integration tests confirm channels actually call their renderer.
Renderers are pure functions of the payload - no network, no
state, fully testable without mocking I/O. The future MQTT
publisher will instantiate WebhookRenderer directly.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
