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  outdated "API 不可用自动降级到本地关键词提取" claims; align with the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

BEHAVIOR_SPEC.md

@@ -508,7 +508,7 @@ Claude 决策: hold / grow / 自动
                     YAML frontmatter:
                       id, name, tags, domain, valence, arousal,
                       importance, type="dynamic", created, last_active,
-                      activation_count=1
+                      activation_count=0   # B-04: starts at 0; touch() bumps to 1+
                                │
                                ▼
           ┌─────── 记忆桶存活期 ──────────────────────────────────────┐