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

client/src/components/settings/HomeDirSetting.tsx

@@ -1,8 +1,9 @@
 /**
  * @file HomeDirSetting.tsx
  * @description One editable home directory (CLAUDE_HOME in Claude Code →
- * AgentHub, CODEX_HOME in Codex → AgentHub): a path field with Save, the
- * server's refusal inline, the value in effect, and a warning when the real
+ * Overview, CODEX_HOME in Codex → Overview): a path field with Save, the
+ * server's refusal inline, the saved value while the field differs from it,
+ * and a warning when the real
  * environment sets the variable (the environment wins at the next start, so a
  * saved value would not survive a restart). The server validates and persists;
  * this component only loads, submits and reports.
@@ -105,7 +106,8 @@ export function HomeDirSetting({ id, title, description, note, placeholder, load
           </button>
         </div>
         {error && <p className="text-xs text-status-danger">{error}</p>}
-        {current && (
+        {/* The saved value, only while the field says something else. */}
+        {current && input !== current.value && (
           <p className="text-xs text-fg-muted">
             {t("homeDir.current")} <code className="text-fg-secondary">{current.value}</code>
           </p>