Configure Gitea Actions for Helm chart CI and release

- Replace GitHub chart-releaser with Gitea-compatible workflow
- Lint job: helm lint, template validation on push to main/master
- Release job: package and publish to Gitea releases on tag push (v*)
- Use gitea-release-action for creating releases
- Support both main and master branches

Co-authored-by: Cursor <cursoragent@cursor.com>

fleetdm-stack/templates/fleet-secret.yaml

@@ -0,0 +1,15 @@
+# Fleet server expects secret "fleet" (S3, TLS). Self-signed cert for local dev.
+apiVersion: v1
+kind: Secret
+metadata:
+  name: fleet
+  labels:
+    app.kubernetes.io/name: fleetdm-stack
+type: Opaque
+stringData:
+  s3-bucket: ""
+  software-installers: ""
+  server.cert: |
+{{ .Files.Get "certs/cert.pem" | nindent 4 }}
+  server.key: |
+{{ .Files.Get "certs/key.pem" | nindent 4 }}