feat: make max_connections configurable via [server] section

The concurrent connection limit was hardcoded to 10,000.
Add server.max_connections config option (default: 10000, 0 = unlimited).

src/config/defaults.rs

@@ -147,6 +147,10 @@ pub(crate) fn default_proxy_protocol_header_timeout_ms() -> u64 {
     500
 }
 
+pub(crate) fn default_server_max_connections() -> u32 {
+    10_000
+}
+
 pub(crate) fn default_prefer_4() -> u8 {
     4
 }

src/config/types.rs

@@ -1167,6 +1167,11 @@ pub struct ServerConfig {
 
     #[serde(default)]
     pub listeners: Vec<ListenerConfig>,
+
+    /// Maximum number of concurrent client connections.
+    /// 0 means unlimited.
+    #[serde(default = "default_server_max_connections")]
+    pub max_connections: u32,
 }
 
 impl Default for ServerConfig {
@@ -1184,6 +1189,7 @@ impl Default for ServerConfig {
             metrics_whitelist: default_metrics_whitelist(),
             api: ApiConfig::default(),
             listeners: Vec::new(),
+            max_connections: default_server_max_connections(),
         }
     }
 }

src/maestro/mod.rs

@@ -349,8 +349,13 @@ pub async fn run() -> std::result::Result<(), Box<dyn std::error::Error>> {
     let beobachten = Arc::new(BeobachtenStore::new());
     let rng = Arc::new(SecureRandom::new());
 
-    // Connection concurrency limit
+    // Connection concurrency limit (0 = unlimited)
-    let max_connections = Arc::new(Semaphore::new(10_000));
+    let max_connections_limit = if config.server.max_connections == 0 {
+        Semaphore::MAX_PERMITS
+    } else {
+        config.server.max_connections as usize
+    };
+    let max_connections = Arc::new(Semaphore::new(max_connections_limit));
 
     let me2dc_fallback = config.general.me2dc_fallback;
     let me_init_retry_attempts = config.general.me_init_retry_attempts;