feat(browser): W4-C BrowserProvider contract and camofox-browser adapter skeleton

- contracts/browser.ts: provider kind, per-capability {supported, verified} flags,
  session/tab/control-lease rows, NavigationBudget, redacted BrowserSnapshot,
  DownloadArtifact with blob/secret refs, BrowserErrorKind
- adapters/browser: BrowserProvider interface, camofox client (health, capabilities
  static + /openapi.json probe, openSession/navigate/snapshot/screenshot; rest
  not_implemented for M2), none provider, redactSnapshot, profile serial lock,
  domain allowlist budget; Bearer access key via BrowserSecretResolver
- testkit/browser: mock camofox server (auth, fixtures with secrets, faults)
- db 0023: browser_provider/session/tab/control_lease with one-active-lease and
  one-live-session-per-profile partial unique indexes; types regenerated
- docs/design/browser-provider.md: contract, camofox OpenAPI 1.17.0 mapping,
  unverified items and M2 prototype checklist; Playwright is not a product browser

Co-Authored-By: Claude Opus 5.5 <[email protected]>

packages/db/test/schema.test.ts

@@ -83,6 +83,11 @@ const EXPECTED_TABLES = [
   "admin_session",
   "login_attempt",
   "sse_event",
+  // W4-C 浏览器实体(0023)
+  "browser_provider",
+  "browser_session",
+  "browser_tab",
+  "browser_control_lease",
 ].sort();
 
 /** 不走 entityTable() 的表:追加型/引擎自有表,没有 uuid id + created_at/updated_at 三件套 */