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.

openapi.yaml

@@ -10700,7 +10700,7 @@ paths:
             type: integer
       responses:
         '200':
-          description: available:true with {branch, head, subject, dirty, untracked}, or available:false alone.
+          description: available:true with {branch, head, subject, dirty, untracked, files}, or available:false alone. files holds the raw `git status --porcelain` lines behind those counts, capped at 20; the counts themselves are never capped.
         '404':
           description: Lane not found.
   /api/lanes/{id}/runtime: