fix: TypeScript errors + workflow pipeline ordering

- Fix hls! null assertions in error handler (TS18047)
- Fix test mock type errors: remove unused errorCall, use (as any) cast
- Pipeline ordering: CD + Pages deploy now run after CI completes (workflow_run: [CI])
- Add GOFLAGS=-mod=mod to playout Docker build for new fsnotify dep

backend/playout/Dockerfile

@@ -6,7 +6,7 @@ COPY src/go.mod src/go.sum ./
 
 # Download dependencies and build
 RUN go mod download
-RUN CGO_ENABLED=0 GOOS=linux go build -o /playlist-manager ./src/playlist.go
+RUN CGO_ENABLED=0 GOOS=linux GOFLAGS=-mod=mod go build -o /playlist-manager ./src/playlist.go
 
 FROM alpine:3.20