feat: add automated install, Docker deployment, and CI Docker job

- debian/control: add Pre-Depends and Depends on postgresql-16, argon2
- debian/postinst: idempotent automation for PostgreSQL setup,
  DB/user creation, migration tracking, admin password generation,
  config write, and service enable/start
- Dockerfile: multi-stage build (Rust + frontend + slim runtime)
- docker/entrypoint.sh: first-run DB wait, migrations, admin password
- docker-compose.yml: split db/app architecture with healthcheck
- .env.example: template for DB_PASSWORD and TAG
- .dockerignore: exclude build artifacts from Docker context
- .github/workflows/ci.yml: add Docker job for multi-arch
  (amd64/arm64) GHCR push on tag releases with layer caching
- .gitignore: add .env entry

Dockerfile

@@ -0,0 +1,111 @@
+# =============================================================================
+# Linux Patch Manager — Multi-stage Docker Build
+# =============================================================================
+# Build:  docker build -t linux-patch-manager .
+# Run:    docker compose up
+# =============================================================================
+
+# ---------------------------------------------------------------------------
+# Stage 1: Rust build
+# ---------------------------------------------------------------------------
+FROM rust:1.82-bookworm AS rust-builder
+
+RUN apt-get update && apt-get install -y \
+    pkg-config \
+    libssl-dev \
+    libfontconfig1-dev \
+    && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /usr/src/app
+
+# Cache dependencies by building a dummy project first
+COPY Cargo.toml Cargo.lock ./
+RUN mkdir -p crates/pm-web/src crates/pm-worker/src crates/pm-core/src \
+    crates/pm-agent-client/src crates/pm-auth/src crates/pm-ca/src \
+    crates/pm-reports/src crates/migrate-secrets/src
+RUN echo 'fn main(){}' > crates/pm-web/src/main.rs \
+    && echo 'fn main(){}' > crates/pm-worker/src/main.rs \
+    && echo '' > crates/pm-core/src/lib.rs \
+    && echo '' > crates/pm-agent-client/src/lib.rs \
+    && echo '' > crates/pm-auth/src/lib.rs \
+    && echo '' > crates/pm-ca/src/lib.rs \
+    && echo '' > crates/pm-reports/src/lib.rs \
+    && echo 'fn main(){}' > crates/migrate-secrets/src/main.rs
+RUN cargo build --release 2>/dev/null || true
+
+# Now build the real project
+COPY crates/ crates/
+RUN cargo build --release
+
+# Verify binaries exist
+RUN ls -la target/release/pm-web target/release/pm-worker
+
+# Strip debug symbols
+RUN strip target/release/pm-web target/release/pm-worker
+
+# ---------------------------------------------------------------------------
+# Stage 2: Frontend build
+# ---------------------------------------------------------------------------
+FROM node:20-bookworm-slim AS frontend-builder
+
+WORKDIR /usr/src/app/frontend
+COPY frontend/package.json frontend/package-lock.json ./
+RUN npm ci --production=false
+
+COPY frontend/ ./
+RUN npm run build
+
+# ---------------------------------------------------------------------------
+# Stage 3: Runtime
+# ---------------------------------------------------------------------------
+FROM debian:bookworm-slim AS runtime
+
+RUN apt-get update && apt-get install -y \
+    ca-certificates \
+    libssl3 \
+    libfontconfig1 \
+    postgresql-client-16 \
+    argon2 \
+    curl \
+    && rm -rf /var/lib/apt/lists/*
+
+# Create service user
+RUN useradd --system --no-create-home --shell /usr/sbin/nologin \
+    --comment "Linux Patch Manager service account" patch-manager
+
+# Create directories
+RUN mkdir -p /etc/patch-manager/ca /etc/patch-manager/certs \
+    /etc/patch-manager/jwt /etc/patch-manager/tls \
+    /var/log/patch-manager /opt/patch-manager \
+    /usr/share/patch-manager/frontend \
+    /usr/share/patch-manager/migrations
+
+# Copy binaries
+COPY --from=rust-builder /usr/src/app/target/release/pm-web /usr/local/bin/pm-web
+COPY --from=rust-builder /usr/src/app/target/release/pm-worker /usr/local/bin/pm-worker
+
+# Copy frontend
+COPY --from=frontend-builder /usr/src/app/frontend/dist/ /usr/share/patch-manager/frontend/
+
+# Copy migrations
+COPY migrations/ /usr/share/patch-manager/migrations/
+
+# Copy entrypoint
+COPY docker/entrypoint.sh /usr/local/bin/entrypoint.sh
+RUN chmod 755 /usr/local/bin/entrypoint.sh
+
+# Copy config template
+COPY config/config.example.toml /usr/share/patch-manager/config.example.toml
+
+# Set ownership
+RUN chown -R patch-manager:patch-manager \
+    /etc/patch-manager /var/log/patch-manager \
+    /opt/patch-manager /usr/share/patch-manager
+
+# Expose HTTPS port
+EXPOSE 443
+
+# Volume for persistent data
+VOLUME ["/etc/patch-manager", "/var/log/patch-manager", "/opt/patch-manager"]
+
+ENTRYPOINT ["/usr/local/bin/entrypoint.sh"]