runShell and runClaude fail with "Case path not found" when case directory does not exist

[vika2603]

When ~/codeman-cases/ does not exist (fresh install or first use), clicking "Run Shell" or "Run Claude Code" with the default testcase case fails with:

Error: Case path not found

Root cause (two bugs in session-ui.js)

1. runClaude() (~line 291): When auto-creating a missing case, the response is accessed as createCaseData.case, but POST /api/cases returns { success, data: { case: { name, path } } }. Should be createCaseData.data.case.

2. runShell() (~line 430): No auto-create logic at all. If the case does not exist, it immediately throws. Should mirror runClaude() auto-create behavior.

Steps to reproduce

1. Remove or ensure ~/codeman-cases/ does not exist
2. Start Codeman (npm run dev)
3. Click "Run Shell" with default "testcase" case

Expected: Case directory is auto-created and session starts.
Actual: Error: Case path not found