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

package.json

@@ -159,8 +159,8 @@
     "@homebridge/ciao": "^1.3.4",
     "@line/bot-sdk": "^10.6.0",
     "@lydell/node-pty": "1.2.0-beta.3",
-    "@mariozechner/pi-agent-core": "0.50.7",
-    "@mariozechner/pi-ai": "0.50.7",
+    "@mariozechner/pi-agent-core": "0.50.9",
+    "@mariozechner/pi-ai": "0.50.9",
     "@mariozechner/pi-coding-agent": "0.50.7",
     "@mariozechner/pi-tui": "0.50.7",
     "@mozilla/readability": "^0.6.0",