Upgrade forgejo-runner to v12.8, adopt server.connections, and clean up docs (#338)

## Summary
- consolidate forgejo-runner how-to docs into current cards
- upgrade the k8s forgejo-runner deployment to the latest v12.8.x runner image
- switch the k8s runner from first-boot register flow to declarative server.connections config
- keep the runner image on the native Dagger build path and update the surrounding manifests/secrets

## Notes
- PR opened early for C1 review
- implementation and deployment verification will follow in subsequent commits

Reviewed-on: #338

containers/forgejo-runner/container.py

@@ -13,7 +13,7 @@ from blumeops.containers import (
     oci_labels,
 )
 
-VERSION = "12.7.3"
+VERSION = "12.8.2"
 
 
 async def build(src: dagger.Directory) -> dagger.Container:
@@ -34,7 +34,7 @@ async def build(src: dagger.Directory) -> dagger.Container:
 
     # Stage 2: Runtime
     runtime = alpine_runtime(
-        extra_apk=["git", "bash", "ca-certificates"],
+        extra_apk=["git", "bash", "ca-certificates", "gettext-envsubst"],
         uid=1000,
         gid=1000,
         username="runner",