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/lanes/__tests__/LaneChangesPanel.test.tsx

@@ -321,6 +321,34 @@ describe("LaneChangesPanel", () => {
     expect(screen.getByText("Staged Changes")).toBeInTheDocument();
   });
 
+  it("reads a whole markdown file rendered after Preview, and back as source after Raw", async () => {
+    vi.mocked(api.lanes.gitTree).mockResolvedValue({
+      available: true,
+      path: "",
+      entries: [{ name: "README.md", path: "README.md", dir: false, status: " M" }],
+      truncated: false,
+    });
+    vi.mocked(api.lanes.gitFile).mockResolvedValue({
+      available: true,
+      path: "README.md",
+      rev: "work",
+      binary: false,
+      truncated: false,
+      lines: ["# Hello", "", "- one"],
+      sha: "c".repeat(40),
+    });
+    const user = userEvent.setup();
+    render(<LaneChangesPanel laneId={7} full />);
+    const sidebar = await screen.findByTestId("lane-changes-sidebar");
+    await user.click(await within(sidebar).findByText("README.md"));
+    await screen.findByTestId("lane-file-view");
+    await user.click(screen.getByTestId("lane-file-preview"));
+    expect(screen.getByRole("heading", { name: "Hello" })).toBeInTheDocument();
+    expect(screen.queryByTestId("lane-file-view")).toBeNull();
+    await user.click(screen.getByTestId("lane-file-preview"));
+    expect(await screen.findByTestId("lane-file-view")).toHaveTextContent("# Hello");
+  });
+
   it("at full width shows the tree as a sidebar and opens a file for reading, editing on a click", async () => {
     vi.mocked(api.lanes.gitTree).mockResolvedValue({
       available: true,