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/pages/__tests__/AiToolConfig.test.tsx

@@ -1,7 +1,7 @@
 /**
  * @file AiToolConfig.test.tsx
  * @description The generic per-tool Settings tab: the tool's path, homepage
- * and an Update link into the AI Tools modal; its session count, cost and
+ * and an Update link to Settings → Agents; its session count, cost and
  * lanes; a default-model picker saved through PUT /api/ai-tools/:id; and its
  * catalog-declared config files, edited over the sha they were opened at with
  * the server's refusal shown.
@@ -112,7 +112,7 @@ describe("AiToolConfig", () => {
     expect(screen.queryByRole("link", { name: "other" })).toBeNull();
     expect(screen.getByRole("link", { name: /update/i })).toHaveAttribute(
       "href",
-      "/settings?tool=gemini#ai-tools"
+      "/settings/agents"
     );
     expect(screen.getByText("pricing:google")).toBeInTheDocument();
   });