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/node-worker/config.py

@@ -9,3 +9,8 @@ DEFAULT_VISION = os.getenv("NODE_DEFAULT_VISION", "llava:13b")
 MAX_CONCURRENCY = int(os.getenv("NODE_WORKER_MAX_CONCURRENCY", "2"))
 MAX_PAYLOAD_BYTES = int(os.getenv("NODE_WORKER_MAX_PAYLOAD_BYTES", str(1024 * 1024)))
 PORT = int(os.getenv("PORT", "8109"))
+
+STT_PROVIDER = os.getenv("STT_PROVIDER", "none")
+TTS_PROVIDER = os.getenv("TTS_PROVIDER", "none")
+OCR_PROVIDER = os.getenv("OCR_PROVIDER", "vision_prompted")
+IMAGE_PROVIDER = os.getenv("IMAGE_PROVIDER", "none")