Set DEPLOY_TIMESTAMP from GitLab CI instead of pod metadata

- Update GitLab CI deploy job to set DEPLOY_TIMESTAMP when deploying
- Use 'kubectl set env' to update all pods with same timestamp
- Change deployment.yaml to use static placeholder value
- Update documentation to explain GitLab CI timestamp approach

This ensures all pods show the same deployment time, regardless of:
- Which pod handles the request (with replicas=2)
- When individual pods were created or restarted
- Pod restarts from crashes or rolling updates

The timestamp now represents when the deployment was initiated by GitLab CI,
not when individual pods were created.

.gitlab-ci.yml

@@ -48,8 +48,12 @@ deploy:
   script:
     - kubectl config get-contexts
     - kubectl config use-context towerops/towerops:home-cluster-agent
+    # Set deployment timestamp (ISO 8601 format in UTC)
+    - DEPLOY_TIMESTAMP=$(date -u +"%Y-%m-%dT%H:%M:%SZ")
+    - echo "Deploying at $DEPLOY_TIMESTAMP"
     # Deploy new version (migrations run on app start)
     - kubectl set image deployment/towerops towerops=$CI_REGISTRY_IMAGE:$CI_COMMIT_SHA -n towerops
+    - kubectl set env deployment/towerops DEPLOY_TIMESTAMP=$DEPLOY_TIMESTAMP -n towerops
     - kubectl rollout status deployment/towerops -n towerops --timeout=5m
   environment:
     name: production

k8s/README.md

@@ -14,17 +14,19 @@ For local development, the project root `.envrc` is used by direnv.
 
 ## Deployment Timestamp
 
-The application footer displays the deployment timestamp to track when the current version was deployed. This is automatically set using the Kubernetes Downward API:
+The application footer displays the deployment timestamp to track when the current version was deployed. This is automatically set by GitLab CI during deployment:
 
 ```yaml
-env:
-  - name: DEPLOY_TIMESTAMP
-    valueFrom:
-      fieldRef:
-        fieldPath: metadata.creationTimestamp
+# GitLab CI sets this during deploy
+- kubectl set env deployment/towerops DEPLOY_TIMESTAMP=$(date -u +"%Y-%m-%dT%H:%M:%SZ") -n towerops
 ```
 
-The pod's creation timestamp is injected as an environment variable and displayed in the footer as "Last deployed X ago · YYYY-MM-DD HH:MM:SS UTC".
+All pods in the deployment share the same timestamp (when the deployment was initiated), regardless of when individual pods were created. This is displayed in the footer as "Last deployed X ago · YYYY-MM-DD HH:MM:SS UTC".
+
+For manual deployments without GitLab CI, set the timestamp:
+```bash
+kubectl set env deployment/towerops DEPLOY_TIMESTAMP=$(date -u +"%Y-%m-%dT%H:%M:%SZ") -n towerops
+```
 
 ## Deploying
 

k8s/deployment.yaml

@@ -56,9 +56,7 @@ spec:
                 fieldRef:
                   fieldPath: metadata.namespace
             - name: DEPLOY_TIMESTAMP
-              valueFrom:
-                fieldRef:
-                  fieldPath: metadata.creationTimestamp
+              value: "1970-01-01T00:00:00Z"  # Placeholder, updated by GitLab CI on deploy
             - name: RELEASE_DISTRIBUTION
               value: "name"
             - name: RELEASE_NODE

lib/towerops/application.ex

@@ -52,24 +52,16 @@ defmodule Towerops.Application do
   Returns the deployment timestamp.
 
   In production (Kubernetes), this reads from the DEPLOY_TIMESTAMP environment
-  variable which should be set during deployment. Falls back to compile time
-  in development.
+  variable which is automatically set by GitLab CI during deployment. Falls back
+  to compile time in development.
 
-  Set DEPLOY_TIMESTAMP in your Kubernetes deployment:
-  ```yaml
-  env:
-    - name: DEPLOY_TIMESTAMP
-      value: "2026-01-17T12:34:56Z"
+  The timestamp is set by GitLab CI using:
+  ```bash
+  kubectl set env deployment/towerops DEPLOY_TIMESTAMP=$(date -u +"%Y-%m-%dT%H:%M:%SZ") -n towerops
   ```
 
-  Or use a downward API to inject the pod creation time:
-  ```yaml
-  env:
-    - name: DEPLOY_TIMESTAMP
-      valueFrom:
-        fieldRef:
-          fieldPath: metadata.creationTimestamp
-  ```
+  This ensures all pods in the deployment show the same deployment time, regardless
+  of when individual pods were created or restarted.
   """
   @spec build_timestamp() :: DateTime.t()
   def build_timestamp do