fix: CI/CD test failures and invalid Go version

- Fix go.mod Go version from invalid 1.25.7 to 1.23
- Fix Dockerfile golang image from 1.25 to 1.23
- Add window.matchMedia mock for jsdom themeStore tests
- Exclude e2e/ from Vitest to prevent Playwright test conflicts
- Add frontend test step to both CI workflows

excalidraw-full.Dockerfile

@@ -0,0 +1,48 @@
+# ===================================================================
+# Excalidraw FULL - Production Dockerfile
+# ===================================================================
+# Builds the new React frontend (not the old excalidraw submodule)
+# and embeds it into the Go binary.
+#
+# Usage:
+#   docker build -f excalidraw-full.Dockerfile -t excalidraw-full .
+#   docker run -p 3002:3002 -v $(pwd)/.env:/root/.env excalidraw-full
+# ===================================================================
+
+# -------------------------------------------------------------------
+# Stage 1: Frontend build
+# -------------------------------------------------------------------
+FROM --platform=$BUILDPLATFORM node:20-alpine AS frontend-builder
+WORKDIR /app/frontend
+COPY frontend/package.json frontend/package-lock.json* ./
+RUN npm install --legacy-peer-deps
+COPY frontend/ ./
+RUN npm run build
+
+# -------------------------------------------------------------------
+# Stage 2: Backend build
+# -------------------------------------------------------------------
+FROM --platform=$BUILDPLATFORM golang:1.23-alpine AS backend-builder
+RUN apk add --no-cache git ca-certificates
+WORKDIR /app
+COPY go.mod go.sum ./
+RUN go mod download
+COPY . .
+# Replace frontend source with built dist so only production assets are embedded
+RUN rm -rf ./frontend && mkdir -p ./frontend
+COPY --from=frontend-builder /app/frontend/dist ./frontend
+ARG TARGETOS
+ARG TARGETARCH
+RUN CGO_ENABLED=0 GOOS=$TARGETOS GOARCH=$TARGETARCH go build -ldflags="-s -w" -o excalidraw-full .
+
+# -------------------------------------------------------------------
+# Stage 3: Final runtime
+# -------------------------------------------------------------------
+FROM alpine:latest
+RUN apk --no-cache add ca-certificates wget
+WORKDIR /root/
+COPY --from=backend-builder /app/excalidraw-full .
+EXPOSE 3002
+HEALTHCHECK --interval=30s --timeout=5s --start-period=5s --retries=3 \
+  CMD wget --no-verbose --tries=1 -O- http://localhost:3002/api/health || exit 1
+CMD ["./excalidraw-full"]