feat(forgejo): enable SMTP email notifications via Gmail

- mailer config: smtp+starttls to smtp.gmail.com:587
- SMTP creds via forgejo-smtp secret (SOPS-encrypted, Gmail App Password)
- Env var injection: GITEA__MAILER__USER/PASSWD from secret
- Enables CI completion emails, password reset, repo notifications

k8s/bootstrap/phase3-forgejo/forgejo-values.yaml

@@ -80,6 +80,14 @@ gitea:
     actions:
       ENABLED: true
 
+    mailer:
+      ENABLED: true
+      PROTOCOL: smtp+starttls
+      SMTP_ADDR: smtp.gmail.com
+      SMTP_PORT: 587
+      FROM: "Forgejo <[email protected]>"
+      # USER and PASSWD injected via env vars below (GITEA__MAILER__USER, GITEA__MAILER__PASSWD)
+
 # Persistence (shared storage for repos)
 persistence:
   enabled: true
@@ -148,3 +156,13 @@ deployment:
         secretKeyRef:
           name: forgejo-db-app
           key: password
+    - name: GITEA__MAILER__USER
+      valueFrom:
+        secretKeyRef:
+          name: forgejo-smtp
+          key: user
+    - name: GITEA__MAILER__PASSWD
+      valueFrom:
+        secretKeyRef:
+          name: forgejo-smtp
+          key: password