ci: fix Dockerfile for Rust + correct Forgejo runner labels

Issues fixed:
- Dockerfile was Python/Uvicorn (wrong for Rust project)
  - Changed to multi-stage Rust build (rust:1.81 → debian:bookworm-slim)
  - Correct binary name: mem (not mem-cli)
  - Added proper health check with curl

- CI runner labels were incorrect (rust/golang → docker)
  - Changed test job to: runs-on: docker with rust:1.81-bookworm container
  - Changed build job to: runs-on: docker

- Docker build config was broken
  - Switched to standard actions (setup-buildx, login, build-push)
  - Added Cargo caching (registry, git, target)
  - Added format + clippy checks
  - Simplified login/build/push flow

Ready for CI/CD pipeline restart.

Dockerfile

@@ -1,53 +1,38 @@
-# Build stage
-FROM rust:1-slim-bookworm AS builder
+# Multi-stage build for Poimen Memory Service (Rust)
 
-WORKDIR /app
+# Stage 1: Builder
+FROM rust:1.81-bookworm as builder
 
-# Install build dependencies
-RUN apt-get update && apt-get install -y \
-    pkg-config \
-    libssl-dev \
-    g++ \
-    && rm -rf /var/lib/apt/lists/*
+WORKDIR /build
 
-# Copy manifests, source, and compile-time assets
-COPY Cargo.toml Cargo.lock ./
-RUN mkdir -p src && echo '// workspace root' > src/lib.rs
-COPY crates ./crates
-COPY templates ./templates
+# Copy source
+COPY . .
 
-# Build release binary
-RUN cargo build --release -p mem-cli --bin mem
+# Build in release mode
+RUN cargo build --release
 
-# Runtime stage
+# Stage 2: Runtime
 FROM debian:bookworm-slim
 
 WORKDIR /app
 
 # Install runtime dependencies
-RUN apt-get update && apt-get install -y \
+RUN apt-get update && apt-get install -y --no-install-recommends \
     ca-certificates \
     libssl3 \
+    postgresql-client \
+    curl \
     && rm -rf /var/lib/apt/lists/*
 
 # Copy binary from builder
-COPY --from=builder /app/target/release/mem /usr/local/bin/mem
+COPY --from=builder /build/target/release/mem /app/mem
 
-# Copy templates and queries
-COPY templates ./templates
-COPY queries ./queries
-
-# Create non-root user
-RUN useradd -r -u 1000 memuser
-USER memuser
-
-# Default port
+# Expose port
 EXPOSE 8080
 
 # Health check
-HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
-    CMD curl -f http://localhost:8080/health || exit 1
+HEALTHCHECK --interval=10s --timeout=5s --start-period=10s --retries=3 \
+  CMD curl -f http://localhost:8080/health || exit 1
 
-# Default command: start HTTP server
-ENTRYPOINT ["mem"]
-CMD ["serve", "--port", "8080"]
+# Run
+CMD ["/app/mem"]