feat(system): add systemd service and installation script

- Add gitks systemd service unit file with security sandboxing
- Create environment configuration template for gitks service
- Add logrotate configuration for gitks application logs
- Implement installation script with service user creation
- Set up proper directory permissions and file ownership
- Configure automatic service startup and systemd integration

etc/gitks.env

@@ -0,0 +1,35 @@
+# GitKS environment configuration
+# 
+# This file is sourced by systemd via EnvironmentFile.
+# Uncomment and adjust values as needed.
+#
+# Location: /etc/gitks/gitks.env
+# Permissions: 0640 root:gitks
+
+REPO_PREFIX_PATH=/data/repos
+GITKS_HOST=0.0.0.0
+GITKS_PORT=50051
+# GITKS_ADVERTISE_ADDR=http://node1.example.com:50051
+GITKS_METRICS_PORT=9100
+
+GITKS_CLUSTER_PORT=4697
+GITKS_CLUSTER_COOKIE=gitks-default-cookie
+# GITKS_CLUSTER_HOSTNAME=node1.example.com
+GITKS_ETCD_ENDPOINTS=http://localhost:2379
+GITKS_ETCD_CONNECT_TIMEOUT=5000
+GITKS_LEASE_TTL=15
+GITKS_HEALTH_CHECK_INTERVAL=1
+GITKS_MAX_HEALTH_FAILURES=10
+GITKS_DISK_CACHE_ENABLED=false
+GITKS_DISK_CACHE_MAX_AGE=300
+GITKS_PACK_CACHE_ENABLED=false
+GITKS_PACK_CACHE_BACKPRESSURE=true
+GITKS_HOOKS_ENABLED=true
+GITKS_HOOK_TIMEOUT=30
+GITKS_ALLOW_CUSTOM_HOOKS=true
+# GITKS_SERVER_HOOKS_DIR=/etc/gitks/hooks
+# GITKS_HOOK_CALLBACK_ADDR=http://localhost:50052
+GITKS_RATE_LIMIT_MAX_CONCURRENT=200
+
+# === LOGGING ===
+RUST_LOG=info