[Bug]: GetLatestSession() does not get latest session

[noahlwest]

• OS: Debian
• kubectl-ai version (run kubectl-ai version): built from head (105eeba)
• LLM provider: Any (confirmed with gemini)
• LLM model: gemini-2.5-pro

GetLatestSession() returns the 1st session sorted by name, which won't necessarily be the latest session

Steps to reproduce the behavior:

1. Run kubectl-ai
2. Try to load session by "latest"
3. Do not get the latest session

Expected behavior
GetLatestSession should get the latest session, (and any functionality that uses GetLatestSession, such as trying to load the 'latest' session).

Additional context
#497 Has an issue with creating session tests related to GetLatestSession.