automc: schema-fit query + CI + FORK doc

- pgsync.go: filter rows where enabled IS NOT FALSE and domain IS NOT NULL,
  matching the existing automc servers table (domain nullable, enabled
  defaults true). Trigger doc now includes UPDATE OF enabled.
- .gitea/workflows/ci.yaml: build/test on push to automc branch + tags,
  publish container as git.timemachine.center/timemachine/mc-router:automc.
- FORK.md: soft-fork relationship doc at repo root.
- docs/AUTOMC.md: quick-start recipe, troubleshooting table,
  sync-lifecycle and waker-dispatch sequence diagrams.

internal/automc/pgsync.go

@@ -82,7 +82,7 @@ func (s *syncer) connectAndLoop(ctx context.Context) error {
 }
 
 func (s *syncer) refresh(ctx context.Context, conn *pgx.Conn) error {
-	rows, err := conn.Query(ctx, `SELECT name, domain, address FROM servers WHERE domain != '' AND address != ''`)
+	rows, err := conn.Query(ctx, `SELECT name, domain, address FROM servers WHERE domain IS NOT NULL AND domain != '' AND address != '' AND enabled IS NOT FALSE`)
 	if err != nil {
 		return err
 	}