fix(agents): update cacheControlTtl to cacheRetention for pi-ai 0.50.9

- Update @mariozechner/pi-ai and pi-agent-core to 0.50.9
- Rename cacheControlTtl to cacheRetention with values none/short/long
- Add backwards compatibility mapping: 5m->short, 1h->long
- Remove dead OpenRouter check (uses openai-completions API)
- Default new configs to cacheRetention: short

src/config/config.pruning-defaults.test.ts

@@ -100,8 +100,8 @@ describe("config pruning defaults", () => {
       expect(cfg.agents?.defaults?.contextPruning?.ttl).toBe("1h");
       expect(cfg.agents?.defaults?.heartbeat?.every).toBe("30m");
       expect(
-        cfg.agents?.defaults?.models?.["anthropic/claude-opus-4-5"]?.params?.cacheControlTtl,
-      ).toBe("1h");
+        cfg.agents?.defaults?.models?.["anthropic/claude-opus-4-5"]?.params?.cacheRetention,
+      ).toBe("short");
     });
   });