feat(settings): one page per section with a grouped nav and search

Settings moves from a tab bar to /settings/<section>: a left nav grouped
General / Agents / Routing / Git / Projects (a select on narrow screens), a
search box over every section (Ctrl/Cmd+F, Enter opens the first match), and
row primitives. Each AI tool has its page under agents/<id>, the AI Tools
modal becomes the Agents page, Pricing shows every vendor, Git → Worktrees
sets which untracked worktrees the sidebar lists, and each project gets a
page with its own worktree override and Forget all. ?tool= and #ai-tools
links redirect to the path form.

client/src/components/lanes/__tests__/AddLaneModal.test.tsx

@@ -826,7 +826,7 @@ describe("AddLaneModal — tool selection", () => {
     expect(await screen.findByText(/No AI tool is installed and enabled/)).toBeInTheDocument();
     expect(screen.getByRole("link", { name: /AI Tools/ })).toHaveAttribute(
       "href",
-      "/settings#ai-tools"
+      "/settings/agents"
     );
   });