feat(agent): web.search / web.fetch via Brave Search (WEB-1)

- adapters/websearch: Brave client (X-Subscription-Token, error classes),
  result normalization with redaction/truncation, SSRF guard, HTML→text fetch
  (10s, 512KB, text/html|text/plain only)
- modules/websearch: 10-min PG cache (region websearch), cross-process
  per-minute limit, web.fetch allowlist = URLs from the caller's latest
  web.search; POST /websearch/test
- settings.agent.webSearch (key write-only → secret_ref); settings card
  under Agent; web.* offered to the model only when enabled, plus a system
  prompt rule; outputs marked untrusted
- capability count 27 → 29; e2e E13; runbook docs/runbook/websearch.md

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

docs/design/glossary.md

@@ -39,6 +39,7 @@
 | AgentRun 被中止 | 停止;状态"已停止" | 中止、取消 |
 | AutomationGrant | 持续授权 | 自动化授权、automation_grant |
 | agent.plan 的步骤清单 | 步骤;进度写"步骤 2/5" | 计划(计划只指下载计划 / 整理计划)、TODO、任务列表 |
+| web.search / web.fetch | 网页搜索 / 读取网页;设置卡叫"网页搜索",提供方叫"搜索服务" | 联网、上网、爬取、网络代理 |
 | agent.propose_options | 方案;动作叫"选定",都不要叫"退回" | 选项、提案 |
 | scope.proposeFirst | 先看方案再执行 | 只要方案、只给方案、plan_only 模式 |
 | 工作流引擎的一次执行 | 运行 | run |