Increase CPU limits to fix SSL connection timeouts (#96)

Pods were running at 500m/500m (100% of limit) with 44-47% of scheduling
periods being CPU-throttled. SSL decryption is CPU-intensive — when the
BEAM gets throttled mid ssl_gen_statem:call/2, the SSL recv stalls until
the cgroup allows CPU again, causing the 15s DBConnection timeout.

This was the actual root cause of "client timed out because it queued
and checked out the connection for longer than 15000ms" errors. Previous
fixes (TCP keepalive, pool tuning, oban pruner) were treating symptoms.

- CPU limit: 500m → 2000m (4 cores burst capacity)
- CPU request: 100m → 500m (guarantee adequate baseline)

Reviewed-on: graham/towerops-web#96

k8s/deployment.yaml

@@ -212,10 +212,10 @@ spec:
           resources:
             requests:
               memory: "1.5Gi"
-              cpu: "100m"
+              cpu: "500m"
             limits:
               memory: "3Gi"
-              cpu: "500m"
+              cpu: "2000m"
           startupProbe:
             httpGet:
               path: /health