feat: migrate to typed messages

- Switch OnMessage → OnTypedMessage with natsutil.Decode[messages.PipelineTrigger]
- Return *messages.PipelineStatus (not map[string]any)
- Remove strVal/mapVal helpers
- Add .dockerignore, GOAMD64=v3 in Dockerfile
- Update tests for typed structs (14 tests pass)

Dockerfile

@@ -14,7 +14,7 @@ RUN go mod download
 COPY . .
 
 # Build static binary
-RUN CGO_ENABLED=0 GOOS=linux go build -ldflags="-w -s" -o /pipeline-bridge .
+RUN CGO_ENABLED=0 GOOS=linux GOAMD64=v3 go build -ldflags="-w -s" -o /pipeline-bridge .
 
 # Runtime stage - scratch for minimal image
 FROM scratch