feat(lanes): name the files behind a lane's uncommitted counts

GET /api/lanes/:id/git now returns `files`, the raw `git status --porcelain`
lines the dirty/untracked counts were already parsed from, capped at 20 so a
lane mid-`npm install` cannot ship thousands of paths through a polled
endpoint. The lane card hovers them as the tooltip on its
"N modified · N untracked" text, appending "… +N" when the cap bit.

No new subprocess and no new endpoint — statusCounts was counting those lines
and throwing them away.

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

@@ -207,6 +207,7 @@ describe("LaneCard git block", () => {
     subject: "free-text rule mode in the form",
     dirty: 2,
     untracked: 1,
+    files: [" M server/lib/alerts.js", " M client/src/lib/api.ts", "?? scratch.txt"],
   };
 
   it("renders the live branch, head, subject and uncommitted counts", async () => {
@@ -218,6 +219,10 @@ describe("LaneCard git block", () => {
     expect(block.textContent).toContain("9b3e74a");
     expect(block.textContent).toContain("free-text rule mode in the form");
     expect(block.textContent).toContain("2");
+    // Hovering the counts names the files behind them.
+    expect(screen.getByText(/modified/).title).toBe(
+      " M server/lib/alerts.js\n M client/src/lib/api.ts\n?? scratch.txt"
+    );
     // The live branch replaces the lane's recorded one rather than doubling it.
     expect(screen.queryByText(/stale\/recorded/)).toBeNull();
   });