test: add unit tests for branches.rs pure functions

[matt2e]

Summary

Add a comprehensive #[cfg(test)] mod tests to branches.rs covering all 13 pure/utility functions with 65 unit tests.

Functions tested

Function	Tests	Coverage
infer_branch_name	8	Spaces, underscores, special chars, dots/slashes, dash collapsing, empty input, numbers, leading/trailing dashes
infer_workspace_name	5	Prefix, slashes, truncation at 32 chars, empty input, dash collapsing
repo_name_from_github_repo	7	Slug extraction, bare names, special chars, dots/underscores, empty after slash, empty string, dash collapsing
validate_workspace_subpath	6	Valid paths, slash/whitespace trimming, empty rejection, dot segments, empty segments, leading slash behavior
normalize_branch_ref	3	Strip origin/ prefix, no prefix, nested paths
resolve_workspace_repo_path	3	home: prefix resolution, nested paths, passthrough
workspace_home_dir	1	Always /home/bloxer
is_worktree_path_exists_error	3	Positive match, negative, empty
is_blox_onboarding_precondition_error	5	Both keywords, onboard only, wrong error type, precondition without onboard
map_blox_status_to_workspace_status	11	All status strings, case insensitivity, stopped/shutting_down while Starting, None/unknown defaults
bootstrap_command_type_name	1	All 4 known types + unknown
parse_git_progress_line	6	Counting/receiving/resolving, no percentage, empty, no colon
fallback_worktree_path_for	3	Non-existent path, suffix appending, skipping occupied suffixes

Changes

• apps/staged/src-tauri/src/branches.rs — added #[cfg(test)] mod tests (+495 lines)
• apps/staged/src-tauri/Cargo.toml — added tempfile = "3" dev-dependency
• Cargo.lock — updated for tempfile