feat: support bare repositories with worktrees

[sQVe]

Summary

Enables lazygit to work with bare Git repositories that use worktrees, fixing crashes when running lazygit from directories containing bare repo + worktree setups. This resolves the "fatal: this operation must be run in a work tree" error that prevents lazygit from starting in these advanced Git workflow scenarios.

Problem solved: Previously, running lazygit in a directory like:

/project/
├── .bare/          # bare repository
├── main/           # worktree for main branch
└── .git            # points to .bare

Would crash with: fatal: this operation must be run in a work tree

Solution: lazygit now detects the bare repo setup and automatically opens in the appropriate worktree (e.g., main branch).

Changes

• Bare repository detection: Added detection logic for common bare repo patterns (.bare, bare.git, .git)
• Worktree selection: Implemented algorithm to automatically select the best worktree, prioritizing default branch, then main/master, then alphabetical order
• Comprehensive test coverage: Added 218 lines of tests covering various bare repo + worktree scenarios including edge cases

Test Plan

For reviewers to verify:

• Test with standard non-bare repositories (existing functionality unchanged)
• Test bare repository with single worktree (should work automatically)
• Test bare repository with multiple worktrees (should select main/master branch worktree)
• Test bare repository with custom default branch (should select correctly)
• Test error handling for invalid/missing bare repositories
• Run existing test suite to ensure no regressions: go test ./pkg/commands/git_commands/
• Test path traversal protection with malicious directory inputs