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  outdated "API 不可用自动降级到本地关键词提取" claims; align with the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

README.md

@@ -591,14 +591,14 @@ Dashboard：浏览器打开 `http://localhost:8000/dashboard`
 > **Free tier won't work**: Render free tier has **no persistent disk** — all memory data is lost on restart. It also sleeps on inactivity. **Starter plan ($7/mo) or above is required.**
 
 项目根目录已包含 `render.yaml`，点击按钮后：
-1. （可选）设置 `OMBRE_API_KEY`：任何 OpenAI 兼容 API 的 key，不填则自动降级为本地关键词提取
+1. 设置 `OMBRE_API_KEY`：任何 OpenAI 兼容 API 的 key（**必需**，未设置时 hold/grow 会报错、仅检索类工具可用）
 2. （可选）设置 `OMBRE_BASE_URL`：API 地址，支持任意 OpenAI 化地址，如 `https://api.deepseek.com/v1` / `http://123.1.1.1:7689/v1` / `http://your-ollama:11434/v1`
 3. Render 自动挂载持久化磁盘到 `/opt/render/project/src/buckets`
 4. Dashboard：`https://<你的服务名>.onrender.com/dashboard`
 5. 部署后 MCP URL：`https://<你的服务名>.onrender.com/mcp`
 
 `render.yaml` is included. After clicking the button:
-1. (Optional) `OMBRE_API_KEY`: any OpenAI-compatible key; omit to fall back to local keyword extraction
+1. `OMBRE_API_KEY`: any OpenAI-compatible key (**required** for hold/grow; without it those tools raise an error)
 2. (Optional) `OMBRE_BASE_URL`: any OpenAI-compatible endpoint, e.g. `https://api.deepseek.com/v1`, `http://123.1.1.1:7689/v1`, `http://your-ollama:11434/v1`
 3. Persistent disk auto-mounts at `/opt/render/project/src/buckets`
 4. Dashboard: `https://<your-service>.onrender.com/dashboard`
@@ -620,7 +620,7 @@ Dashboard：浏览器打开 `http://localhost:8000/dashboard`
    - Zeabur auto-detects the `Dockerfile` in root and builds via Docker
 
 2. **设置环境变量 / Set environment variables**（服务页面 → **Variables** 标签页）
-   - `OMBRE_API_KEY`（可选）— LLM API 密钥，不填则自动降级为本地关键词提取
+   - `OMBRE_API_KEY`（**必需**）— LLM API 密钥；未设置时 hold/grow/dream 会报错
    - `OMBRE_BASE_URL`（可选）— API 地址，如 `https://api.deepseek.com/v1`
 
    > ⚠️ **不需要**手动设置 `OMBRE_TRANSPORT` 和 `OMBRE_BUCKETS_DIR`，Dockerfile 里已经设好了默认值。Zeabur 对单阶段 Dockerfile 会自动注入控制台设置的环境变量。