perf: optimize worktree entry latency

[wasabeef]

Summary

• avoid full worktree status scans for create by introducing has_linked_worktrees
• add BasicWorktreeInfo and use list_worktrees_basic for batch delete, rename, switch, and search
• preserve existing behavior with regression tests for first-worktree prompts, renamed worktree identity, candidate ordering, and switch path handling

Validation

• cargo fmt --check
• cargo clippy --all-features -- -D warnings
• cargo test --all-features -- --test-threads=1

[github-actions]

Code Metrics Report

Coverage	Test Execution Time
68.6%	2m15s

Code coverage of files in pull request scope (71.7%)

Files	Coverage
src/infrastructure/git.rs	72.4%
src/usecases/create_worktree.rs	70.9%
src/usecases/delete_worktree.rs	59.4%
src/usecases/rename_worktree.rs	84.6%
src/usecases/search_worktrees.rs	47.0%
src/usecases/switch_worktree.rs	90.4%

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Reported by octocov