Link support codes to agent sessions

- Server: Accept support_code param in WebSocket connection
- Server: Link code to session when agent connects, mark as connected
- Server: Mark code as completed when agent disconnects
- Agent: Accept support code from command line argument
- Agent: Send hostname and support_code in WebSocket params
- Portal: Trigger agent download with code in filename
- Portal: Show code reminder in download instructions
- Dashboard: Add machines list fetching (Access tab)
- Add TODO.md for feature tracking

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

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

agent/src/session/mod.rs

@@ -46,10 +46,13 @@ impl SessionManager {
     pub async fn connect(&mut self) -> Result<()> {
         self.state = SessionState::Connecting;
 
+        let hostname = self.config.hostname();
         let transport = WebSocketTransport::connect(
             &self.config.server_url,
             &self.config.agent_id,
             &self.config.api_key,
+            Some(&hostname),
+            self.config.support_code.as_deref(),
         ).await?;
 
         self.transport = Some(transport);