refactor: doc/code consistency, OMBRE_PORT, webhook push, host-vault dashboard

Doc-code consistency (per BEHAVIOR_SPEC.md ground truth):
- INTERNALS.md, dehydrator.py, README.md, config.example.yaml: drop the
  outdated "API 不可用自动降级到本地关键词提取" claims; align with the
  "RuntimeError on API outage, no silent fallback" design decision
- INTERNALS.md & BEHAVIOR_SPEC.md narrative: activation_count=1 → 0 (B-04)
- server.py header: 5 MCP tools → 6 (add dream)

OMBRE_PORT (T5/T6):
- Replace hardcoded 8000 in FastMCP / uvicorn / keepalive URL
  with int(os.environ.get("OMBRE_PORT", "8000"))

OMBRE_HOOK_URL / OMBRE_HOOK_SKIP webhook (T7):
- Implement _fire_webhook() helper: fire-and-forget POST with 5s timeout,
  failures logged at WARNING but never propagated
- Wired into breath / dream MCP tools and /breath-hook + /dream-hook routes
- Push payload: {event, timestamp, payload:{...}}; documented in ENV_VARS.md

Dashboard host-vault input (T12, per user request):
- New /api/host-vault GET/POST endpoints persist OMBRE_HOST_VAULT_DIR
  to project-root .env (idempotent upsert, preserves other entries,
  rejects quotes/newlines)
- Settings tab gains a "宿主机记忆桶目录 (Docker)" panel with
  load/save buttons and a clear "需要 docker compose down/up 生效" notice

config.example.yaml

@@ -28,9 +28,11 @@ log_level: "INFO"
 merge_threshold: 75
 
 # --- Dehydration API / 脱水压缩 API 配置 ---
-# Uses a cheap LLM for intelligent compression; auto-degrades to local
-# keyword extraction if API is unavailable
-# 用廉价 LLM 做智能压缩，API 不可用时自动降级到本地关键词提取
+# Uses a cheap LLM for intelligent compression. API is required; if the
+# configured key/endpoint is unavailable, hold/grow will raise an explicit
+# error instead of silently degrading (see BEHAVIOR_SPEC.md 三、降级行为表).
+# 用廉价 LLM 做智能压缩。API 为必需；如 key/endpoint 不可用，
+# hold/grow 会直接报错而非静默降级（详见 BEHAVIOR_SPEC.md 三、降级行为表）。
 dehydration:
   # Supports any OpenAI-compatible API: DeepSeek / Ollama / LM Studio / vLLM / Gemini etc.
   # 支持所有 OpenAI 兼容 API：DeepSeek / Ollama / LM Studio / vLLM / Gemini 等