feat: display app version in UI footer

- Add version package with build-time variables
- Inject version via ldflags in Dockerfile using git describe
- Show version in footer on every page
- Log version and commit on server startup

Dockerfile

@@ -1,5 +1,8 @@
 FROM docker.io/golang:1.25.4-alpine AS build
 
+ARG VERSION=dev
+ARG COMMIT=unknown
+
 RUN apk add --no-cache upx
 
 WORKDIR /src
@@ -10,7 +13,8 @@ COPY . .
 RUN go tool templ generate
 RUN go tool gotailwind -i assets/css/input.css -o assets/css/output.css --minify
 RUN --mount=type=cache,target=/root/.cache/go-build \
-    CGO_ENABLED=0 go build -ldflags="-s" -o /bin/games .
+    MODULE=$(head -1 go.mod | awk '{print $2}') && \
+    CGO_ENABLED=0 go build -ldflags="-s -X $MODULE/version.Version=$VERSION -X $MODULE/version.Commit=$COMMIT" -o /bin/games .
 RUN upx -9 -k /bin/games
 
 FROM scratch