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/App.tsx

@@ -103,11 +103,11 @@ export default function App() {
             <Route path="lanes" element={<Navigate to="/workspace" replace />} />
             <Route
               path="cc-config"
-              element={<Navigate to="/settings?tool=claude-code" replace />}
+              element={<Navigate to="/settings/agents/claude-code" replace />}
             />
             <Route path="run" element={<Navigate to="/workspace" replace />} />
             <Route path="workspace" element={<Workspace />} />
-            <Route path="settings" element={<SettingsHub />} />
+            <Route path="settings/*" element={<SettingsHub />} />
             <Route path="*" element={<NotFound />} />
           </Route>
         </Routes>