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/i18n/locales/en/lanes.json

@@ -53,8 +53,7 @@
   "addLaneSetupTitle": "Setup",
   "addLaneTitleLabel": "Title",
   "addLaneTitlePlaceholder": "Optional",
-  "addLaneToolDefault": "Default ({{tool}})",
-  "addLaneToolOther": "Other…",
+  "addLaneToolDefaultBadge": "Default",
   "addLaneNoTools": "No AI tool is installed and enabled.",
   "addLaneNoToolsLink": "Open Settings → AI Tools",
   "addLaneRouterNativeTool": "Native ({{tool}})",
@@ -258,6 +257,8 @@
   "changes.save": "Save",
   "changes.cancelEdit": "Cancel",
   "changes.clickToEdit": "Click the text to edit",
+  "changes.preview": "Preview",
+  "changes.raw": "Raw",
   "changes.editorLabel": "Edit {{path}}",
   "changes.prevHunk": "Previous change",
   "changes.nextHunk": "Next change",