pipeline: equal-width columns + per-column clear/stop button

Extract a ColumnShell component so all four columns share the same flex-1
basis-0 width (no more 24/16/18/16 rem mix) and the same header layout
(title + count + optional action button on the right).

Per-column actions:
- Review:     'Skip all' → POST /api/review/skip-all (new endpoint, sets all
              pending non-noop plans to skipped in one update)
- Queued:     'Clear'    → POST /api/execute/clear (existing; cancels pending jobs)
- Processing: 'Stop'     → POST /api/execute/stop (new; SIGTERMs the running
              ffmpeg via a tracked Bun.spawn handle, runJob's catch path
              marks the job error and cleans up)
- Done:       'Clear'    → POST /api/execute/clear-completed (existing)

All destructive actions confirm before firing.

server/api/review.ts

@@ -632,6 +632,16 @@ app.post("/:id/unapprove", (c) => {
 
 // ─── Skip / Unskip ───────────────────────────────────────────────────────────
 
+app.post("/skip-all", (c) => {
+	const db = getDb();
+	const result = db
+		.prepare(
+			"UPDATE review_plans SET status = 'skipped', reviewed_at = datetime('now') WHERE status = 'pending' AND is_noop = 0",
+		)
+		.run();
+	return c.json({ ok: true, skipped: result.changes });
+});
+
 app.post("/:id/skip", (c) => {
 	const db = getDb();
 	const id = parseId(c.req.param("id"));