Phase 1: Foundation - CI/CD, systemd service, test framework

Completed Phase 1 foundation tasks:
- CI/CD pipeline (.github/workflows/ci.yml)
  - Format check (rustfmt)
  - Clippy lints
  - Unit tests with codecov
  - Security audit (cargo-audit)
  - Build release artifacts
  - Ubuntu package build
- Systemd service file (configs/linux-patch-api.service)
  - Security hardening (ProtectSystem, SystemCallFilter)
  - Journal logging integration
  - Resource limits
- Test framework structure (tests/unit/, tests/integration/)
  - Initial unit test template
  - Test framework verified with cargo test

Rust toolchain 1.94.1 installed and verified.

configs/linux-patch-api.service

@@ -0,0 +1,57 @@
+[Unit]
+Description=Linux Patch API - Secure Remote Package Management
+Documentation=man:linux-patch-api(8)
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=notify
+ExecStart=/usr/bin/linux-patch-api --config /etc/linux_patch_api/config.yaml
+Restart=on-failure
+RestartSec=5s
+TimeoutStopSec=30s
+
+# Process management
+RuntimeDirectory=linux-patch-api
+RuntimeDirectoryMode=0755
+
+# Security hardening
+NoNewPrivileges=true
+ProtectSystem=strict
+ProtectHome=true
+ReadWritePaths=/var/lib/linux_patch_api /var/log/linux_patch_api
+PrivateTmp=true
+PrivateDevices=true
+ProtectHostname=true
+ProtectClock=true
+ProtectKernelTunables=true
+ProtectKernelModules=true
+ProtectKernelLogs=true
+RestrictNamespaces=true
+LockPersonality=true
+MemoryDenyWriteExecute=false
+RestrictRealtime=true
+RestrictSUIDSGID=true
+RemoveIPC=true
+
+# System call filtering (whitelist approach)
+SystemCallFilter=@system-service
+SystemCallErrorNumber=EPERM
+
+# Environment
+Environment="RUST_BACKTRACE=1"
+Environment="RUST_LOG=info"
+
+# Logging
+StandardOutput=journal
+StandardError=journal
+SyslogIdentifier=linux-patch-api
+SyslogFacility=daemon
+SyslogLevel=info
+
+# Resource limits
+LimitNOFILE=65536
+LimitNPROC=4096
+
+[Install]
+WantedBy=multi-user.target