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__/AddLaneModal.test.tsx

@@ -10,7 +10,7 @@
  */
 
 import { describe, it, expect, vi, beforeEach } from "vitest";
-import { render, screen, waitFor } from "@testing-library/react";
+import { render, screen, waitFor, within } from "@testing-library/react";
 import userEvent from "@testing-library/user-event";
 import { AddLaneModal } from "../AddLaneModal";
 import { api } from "../../../lib/api";
@@ -32,7 +32,7 @@ vi.mock("../../../lib/api", () => ({
       routerApply: vi.fn(),
     },
     aiRouters: { list: vi.fn() },
-    aiTools: { list: vi.fn() },
+    aiTools: { list: vi.fn(), iconUrl: (id: string) => `/api/ai-tools/${id}/icon` },
     run: { start: vi.fn() },
   },
 }));
@@ -784,14 +784,20 @@ describe("AddLaneModal — tool selection", () => {
     const dirField = screen.getByLabelText("Directory");
     await focusField(user, dirField);
     await user.type(dirField, "/tmp/demo");
-    const other = await screen.findByRole("combobox", { name: "Other…" });
-    // Installed + enabled only, and never the default itself.
-    expect(Array.from((other as HTMLSelectElement).options).map((o) => o.value)).toEqual([
-      "",
-      "codex",
-      "gemini",
-    ]);
-    await user.selectOptions(other, "codex");
+    // One button showing the default; it opens every installed + enabled tool.
+    const picker = await screen.findByRole("button", { name: /Claude Code.*Default/ });
+    expect(picker).toHaveAttribute("aria-expanded", "false");
+    await user.click(picker);
+    const list = screen.getByRole("group", { name: /Which CLI drives this lane/ });
+    expect(
+      within(list)
+        .getAllByRole("button")
+        .map((b) => b.textContent)
+    ).toEqual(["Claude Code", "Codex", "Gemini"]);
+    await user.click(within(list).getByRole("button", { name: "Codex" }));
+    // The picked tool replaces the default on the button, and the list closes.
+    expect(screen.getByRole("button", { name: "Codex", expanded: false })).toBeInTheDocument();
+    expect(screen.queryByRole("button", { name: "Gemini" })).toBeNull();
     await user.click(screen.getByRole("button", { name: /add lane|create/i }));
 
     await waitFor(() =>
@@ -802,7 +808,8 @@ describe("AddLaneModal — tool selection", () => {
   it("offers only Native for a tool that cannot use an AI Router", async () => {
     renderModal({});
     const user = userEvent.setup();
-    await user.selectOptions(await screen.findByRole("combobox", { name: "Other…" }), "gemini");
+    await user.click(await screen.findByRole("button", { name: /Claude Code.*Default/ }));
+    await user.click(screen.getByRole("button", { name: "Gemini" }));
     expect(screen.getByRole("radio", { name: "Native (Gemini)" })).toBeChecked();
     expect(screen.getByRole("radio", { name: "AI Router" })).toBeDisabled();
   });