feat(campaigns): campaign timing panel with Red/Blue aggregated metrics

Backend: GET /campaigns/{id}/timing-summary
  Aggregates timing across all campaign tests:
  - red_execution_secs: red_started_at → blue_started_at (minus paused)
  - blue_queue_secs:    blue_started_at → blue_work_started_at
  - blue_evaluation_secs: blue_work_started_at → validated (minus paused)
  - total_secs: sum of all three phases
  Returns totals + per-test breakdown sorted by total time desc.

Frontend: new CampaignTimingPanel component replaces WorklogTimeline
  - 4 summary cards: Red Execution / Blue Queue / Blue Evaluation / Total
  - Stacked horizontal bar showing time distribution
  - Per-test breakdown with individual mini-bars and phase durations
  - Shows 'No tests started yet' when no timing data available

frontend/src/api/campaigns.ts

@@ -194,6 +194,37 @@ export async function deleteCampaign(
   });
 }
 
+// ── Timing summary ─────────────────────────────────────────────────
+
+export interface CampaignTimingBreakdown {
+  test_id: string;
+  test_name: string;
+  state: string | null;
+  red_execution_secs: number;
+  blue_queue_secs: number;
+  blue_evaluation_secs: number;
+  total_secs: number;
+  has_timing: boolean;
+}
+
+export interface CampaignTimingSummary {
+  campaign_id: string;
+  campaign_name: string;
+  tests_total: number;
+  tests_with_timing: number;
+  red_execution_secs: number;
+  blue_queue_secs: number;
+  blue_evaluation_secs: number;
+  total_secs: number;
+  breakdown: CampaignTimingBreakdown[];
+}
+
+/** Get aggregated Red/Blue timing metrics for a campaign. */
+export async function getCampaignTiming(campaignId: string): Promise<CampaignTimingSummary> {
+  const { data } = await client.get<CampaignTimingSummary>(`/campaigns/${campaignId}/timing-summary`);
+  return data;
+}
+
 /** Get execution history (child campaigns) for a recurring campaign. */
 export async function getCampaignHistory(campaignId: string): Promise<{
   campaign_id: string;