feat: flight price monitor with Kiwi adapter stub and cron setup

- config.json: BER→EZE route, €700 threshold, 14-28 nights, Dec-Mar preferred
- monitor.py: config-driven, multi-route, windowed date search, openclaw alerts
- adapters/base.py: abstract FlightAdapter interface
- adapters/kiwi.py: Kiwi/Tequila v2 adapter (stub until KIWI_API_KEY is set)
- requirements.txt, cron-install.sh (daily 08:00 UTC), README.md

config.json

@@ -0,0 +1,15 @@
+{
+  "routes": [
+    {
+      "id": "ber-eze",
+      "origin": "BER",
+      "destination": "EZE",
+      "threshold_eur": 700,
+      "min_nights": 14,
+      "max_nights": 28,
+      "preferred_months": [12, 1, 2, 3],
+      "monitor_year_round": true
+    }
+  ],
+  "check_interval_hours": 24
+}