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/lib/types.ts

@@ -2592,6 +2592,8 @@ export type LaneGitFacts =
       dirty: number;
       /** Files git has never seen. */
       untracked: number;
+      /** Raw `git status --porcelain` lines, capped; the counts stay exact. */
+      files: string[];
     }
   | { available: false };