test(analysis): add integration tests for worktree path and findGitRoot

Cover the remaining uncovered code paths:
- resolveEffectiveInput with a real commit (worktree creation + cleanup)
- subdirectory scope preservation in worktree mode
- findGitRoot error when not inside a git repository
- exception cause preservation when both rev-parse and date fallback fail
- date fallback resolution via mock

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>