P3.5-P3.7: 2-layer inventory, capability routing, STT/TTS adapters, Dev Contract

NCS:
- _collect_worker_caps() fetches capability flags from node-worker /caps
- _derive_capabilities() merges served model types + worker provider flags
- installed_artifacts replaces inventory_only (disk scan with DISK_SCAN_PATHS env)
- New endpoints: /capabilities/caps, /capabilities/installed

Node Worker:
- STT_PROVIDER, TTS_PROVIDER, OCR_PROVIDER, IMAGE_PROVIDER env flags
- /caps endpoint returns capabilities + providers for NCS aggregation
- STT adapter (providers/stt_mlx_whisper.py) — remote + local mode
- TTS adapter (providers/tts_mlx_kokoro.py) — remote + local mode
- OCR handler via vision_prompted (ollama_vision with OCR prompt)
- NATS subjects: node.{id}.stt/tts/ocr/image.request

Router:
- POST /v1/capability/{stt,tts,ocr,image} — capability-based offload routing
- GET /v1/capabilities — global view with capabilities_by_node
- require_fresh_caps(ttl) preflight guard
- find_nodes_with_capability(cap) + load-based node selection

Ops:
- ops/fabric_snapshot.py — full runtime snapshot collector
- ops/fabric_preflight.sh — quick check + snapshot save + diff
- docs/fabric_contract.md — Dev Contract v0.1 (preflight-first)
- tests/test_fabric_contract.py — CI enforcement (6 tests)

Made-with: Cursor

services/router/offload_client.py

@@ -81,7 +81,7 @@ def get_unavailable_nodes(req_type: str) -> Set[str]:
 async def offload_infer(
     nats_client,
     node_id: str,
-    required_type: Literal["llm", "vision", "stt", "tts"],
+    required_type: Literal["llm", "vision", "stt", "tts", "ocr", "image"],
     job_payload: Dict[str, Any],
     timeout_ms: int = 25000,
 ) -> Optional[Dict[str, Any]]: