feat: inject build version/commit into scraper and UI at docker build time

- Go scraper: Version/Commit vars in main.go, injected via -ldflags; Server struct + New() updated; GET /health and new GET /api/version expose them
- UI Dockerfile: ARG BUILD_VERSION/BUILD_COMMIT → ENV PUBLIC_BUILD_VERSION/PUBLIC_BUILD_COMMIT for SvelteKit
- Footer: shows version+short commit when not 'dev' (text-zinc-800, subtle)
- docker-compose: args blocks for scraper and ui build sections pass $GIT_TAG/$GIT_COMMIT

scraper/Dockerfile

@@ -9,8 +9,14 @@ RUN go mod download
 
 COPY . .
 
+# Build-time version info — injected by docker-compose or CI via --build-arg.
+ARG VERSION=dev
+ARG COMMIT=unknown
+
 RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 \
-    go build -ldflags="-s -w" -o /scraper ./cmd/scraper
+    go build \
+      -ldflags="-s -w -X main.Version=${VERSION} -X main.Commit=${COMMIT}" \
+      -o /scraper ./cmd/scraper
 
 # ── Runtime stage ──────────────────────────────────────────────────────────────
 FROM alpine:3.21