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/AddLaneModal.tsx

@@ -437,7 +437,7 @@ export function AddLaneModal({
           {noTools ? (
             <p className="rounded-md border border-status-warning/40 bg-status-warning/10 px-2 py-1.5 text-xs text-status-warning">
               {t("addLaneNoTools")}{" "}
-              <a href="/settings#ai-tools" className="underline">
+              <a href="/settings/agents" className="underline">
                 {t("addLaneNoToolsLink")}
               </a>
             </p>