feat(ui): AI Tools modal, one-button lane tool picker, AgentHub settings in Overview, markdown preview

- AI Tools moves from a Settings section into a modal behind a button at the
  Settings tab bar's right edge (AiToolsModal, `actions` on PageTabs,
  /settings#ai-tools); rows get an enable switch, Default badge, and an
  Update button for every tool whose catalog names an updater (no version
  lookup on open); not-installed tools fold behind a disclosure, a finished
  job's log folds to one line; shared AiToolIcon
- codex updates through its own `codex update`, openclaw/hermes gain
  `update --yes`; update-all runs every installed updater and skips an npm
  one only when npm does not manage the binary
- Add-lane tool picker is one button showing the chosen tool that opens the
  enabled tools as buttons
- Claude Code / Codex AgentHub sub-tab folded into Overview (home editor,
  hooks, pricing); the path list drops CLAUDE_HOME/CODEX_HOME;
  HomeDirSetting shows the saved value only while the field differs
- Preview/Raw toggle for markdown files in the config FileViewer and the
  Changes panel's whole-file view (MarkdownPreview: react-markdown +
  remark-gfm, raw HTML never run, frontmatter as a code block)
- docs and the CLAUDE.md marker updated

SETUP.md

@@ -133,10 +133,10 @@ npm run clear-data
 ### Data management via Settings page
 
 The Settings page (`/settings`) provides a UI for the following. **Model Pricing**
-and **Hook Configuration** are not on its Dashboard tab: they live in the Claude
-Code tab's **AgentHub** sub-tab (Settings → Claude Code → AgentHub), beside
-CLAUDE_HOME; Codex and Antigravity have their own pricing and hooks in their
-own tabs.
+and **Hook Configuration** are not on its Dashboard tab: they sit under the
+Claude Code tab's **Overview** (Settings → Claude Code → Overview), beside
+CLAUDE_HOME; Codex (its Overview) and Antigravity have their own pricing and
+hooks in their own tabs.
 
 - **Model Pricing** — view and edit per-model cost rates, reset to defaults, add custom models
 - **Hook Configuration** — check which hooks are installed and reinstall them