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/src/index.ts

@@ -117,6 +117,7 @@ export {
 	parseSessionEntries,
 	type SessionEntry,
 	type SessionHeader,
+	type SessionInfo,
 	SessionManager,
 	type SessionMessageEntry,
 	SUMMARY_PREFIX,