Refactor SessionManager to use static factory methods

- Add factory methods: create(cwd), open(path), continueRecent(cwd), inMemory()
- Add static list(cwd) for session listing
- Make constructor private, pass cwd explicitly
- Update SDK to take sessionManager instead of sessionFile options
- Update main.ts to create SessionManager based on CLI flags
- Update SessionSelectorComponent to take sessions[] instead of SessionManager
- Update tests to use factory methods

packages/coding-agent/test/agent-session-branching.test.ts

@@ -56,10 +56,7 @@ describe.skipIf(!API_KEY)("AgentSession branching", () => {
 			},
 		});
 
-		sessionManager = new SessionManager(false);
-		if (noSession) {
-			sessionManager.disable();
-		}
+		sessionManager = noSession ? SessionManager.inMemory() : SessionManager.create(tempDir);
 		const settingsManager = new SettingsManager(tempDir);
 
 		session = new AgentSession({

packages/coding-agent/test/agent-session-compaction.test.ts

@@ -60,7 +60,7 @@ describe.skipIf(!API_KEY)("AgentSession compaction e2e", () => {
 			},
 		});
 
-		sessionManager = new SessionManager(false);
+		sessionManager = SessionManager.create(tempDir);
 		const settingsManager = new SettingsManager(tempDir);
 
 		session = new AgentSession({
@@ -174,9 +174,8 @@ describe.skipIf(!API_KEY)("AgentSession compaction e2e", () => {
 			},
 		});
 
-		// Create session manager and disable file persistence
-		const noSessionManager = new SessionManager(false);
-		noSessionManager.disable();
+		// Create in-memory session manager
+		const noSessionManager = SessionManager.inMemory();
 
 		const settingsManager = new SettingsManager(tempDir);