cache.rs: make minimal_roots pub(crate); add 8 tests covering the
minimal_roots helper (empty input, single root, nested vs sibling dirs)
and validate_and_update (stale project removal, no-change short-circuit,
mtime-triggered rescan, legacy empty dir_mtimes).
session.rs: make session_name pub(crate); add 5 tests covering session
name sanitisation (dots→underscores, spaces→dashes, fallback for root
path) and TOML parsing for Window and SessionConfig with layout.
config.rs: add 3 tests covering serde defaults when optional fields are
absent, full config parsing and invalid TOML rejection.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Move scan_from_root, scan_all_roots, get_projects, show_cache_status
and launch_tmux_session from main.rs into a new src/lib.rs, making
them pub so they are testable independently of the binary entrypoint.
main.rs is now a thin entrypoint that imports from tmuxido:: and keeps
only select_project_with_fzf (interactive subprocess, not unit-testable).
Add tempfile = "3" to [dev-dependencies] in preparation for tests.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
