Add PostgreSQL database persistence

- Add connect_machines, connect_sessions, connect_session_events, connect_support_codes tables
- Implement db module with connection pooling (sqlx)
- Add machine persistence across server restarts
- Add audit logging for session/viewer events
- Support codes now persisted to database

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

server/src/config.rs

@@ -9,9 +9,12 @@ pub struct Config {
     /// Address to listen on (e.g., "0.0.0.0:8080")
     pub listen_addr: String,
 
-    /// Database URL (optional for MVP)
+    /// Database URL (optional - server works without it)
     pub database_url: Option<String>,
 
+    /// Maximum database connections in pool
+    pub database_max_connections: u32,
+
     /// JWT secret for authentication
     pub jwt_secret: Option<String>,
 
@@ -25,6 +28,10 @@ impl Config {
         Ok(Self {
             listen_addr: env::var("LISTEN_ADDR").unwrap_or_else(|_| "0.0.0.0:8080".to_string()),
             database_url: env::var("DATABASE_URL").ok(),
+            database_max_connections: env::var("DATABASE_MAX_CONNECTIONS")
+                .ok()
+                .and_then(|v| v.parse().ok())
+                .unwrap_or(5),
             jwt_secret: env::var("JWT_SECRET").ok(),
             debug: env::var("DEBUG")
                 .map(|v| v == "1" || v.to_lowercase() == "true")
@@ -38,6 +45,7 @@ impl Default for Config {
         Self {
             listen_addr: "0.0.0.0:8080".to_string(),
             database_url: None,
+            database_max_connections: 5,
             jwt_secret: None,
             debug: false,
         }