Add zero-downtime deployment configuration

Prevent WebSocket disconnections during deployments by:

1. Rolling Update Strategy:
   - maxSurge: 1 (allow 1 extra pod during rollout)
   - maxUnavailable: 0 (keep all pods running)
   - minReadySeconds: 10 (wait before continuing rollout)

2. Graceful Shutdown:
   - terminationGracePeriodSeconds: 30 (allow Phoenix to drain connections)

3. PodDisruptionBudget:
   - minAvailable: 1 (ensure at least 1 pod always available)
   - Prevents all pods from being terminated simultaneously

4. Improved Health Checks:
   - Faster readiness probe (5s initial, 3s period)
   - More aggressive success/failure thresholds
   - New pods marked ready faster

This ensures new pods are fully ready and serving traffic before old
pods are terminated, maintaining WebSocket connections and preventing
'something went wrong' errors during deployments.

k8s/deployment.yaml

@@ -6,6 +6,12 @@ metadata:
   namespace: towerops
 spec:
   replicas: 2
+  strategy:
+    type: RollingUpdate
+    rollingUpdate:
+      maxSurge: 1        # Allow 1 extra pod during rollout
+      maxUnavailable: 0  # Keep all pods running during rollout
+  minReadySeconds: 10    # Wait 10s after pod is ready before continuing
   selector:
     matchLabels:
       app: towerops
@@ -14,6 +20,7 @@ spec:
       labels:
         app: towerops
     spec:
+      terminationGracePeriodSeconds: 30  # Allow 30s for graceful shutdown
       imagePullSecrets:
         - name: gitlab-registry
       securityContext:
@@ -95,9 +102,14 @@ spec:
               port: 4000
             initialDelaySeconds: 30
             periodSeconds: 10
+            timeoutSeconds: 3
+            failureThreshold: 3
           readinessProbe:
             httpGet:
               path: /health
               port: 4000
-            initialDelaySeconds: 10
-            periodSeconds: 5
+            initialDelaySeconds: 5
+            periodSeconds: 3
+            timeoutSeconds: 2
+            successThreshold: 1
+            failureThreshold: 2

k8s/kustomization.yaml

@@ -8,3 +8,4 @@ resources:
   - service-headless.yaml
   - certificate.yaml
   - ingressroute.yaml
+  - poddisruptionbudget.yaml

k8s/poddisruptionbudget.yaml

@@ -0,0 +1,11 @@
+---
+apiVersion: policy/v1
+kind: PodDisruptionBudget
+metadata:
+  name: towerops-pdb
+  namespace: towerops
+spec:
+  minAvailable: 1  # Keep at least 1 pod running during voluntary disruptions
+  selector:
+    matchLabels:
+      app: towerops