Add recursive scanning (-r), plus --version, --min-size, --exclude

[fahadsiddiqui]

Status

Partly resolved by #17. Rewritten to describe what is actually left.

Done on main: flag parsing is wired up. --help works and exits 0, unknown flags exit 2 with a message naming the flag instead of stat --help: no such file or directory, a second positional argument is rejected rather than silently ignored, and --json / --quiet / --no-script exist.

Still open: recursive scanning, and the smaller flags below.

Recursive scanning (-r / --recursive)

The single most likely thing a user wants, and still impossible — scan() is non-recursive by design and only reads the top level of the given directory.

PR #1 implemented this against the old findDuplicates() and was closed when #17 replaced that function; the logic could not be rebased onto a function that no longer exists. The work is smaller now:

• Thread a recursive bool through scanWithProgress() in scan.go.
• Swap os.ReadDir for filepath.WalkDir (not filepath.Walk — WalkDir avoids a per-entry Lstat).
• Skip .git, node_modules, and vendor via fs.SkipDir, with an --exclude PATTERN flag to extend the list.

The exclusion list is not optional

Measured with PR #1's build, on a git repo containing exactly one real file:

files processed under -r:     27
files processed without -r:    1

Twenty-six of those are .git internals. Git objects are content-addressed, so this is both a large amount of wasted I/O and a source of meaningless duplicate groups.

Interaction with #7 — handle in the same change

Priority scoring only looks at filepath.Base, so recursion sharply increases equal-priority ties across directories. Measured with PR #1's build:

✗ DELETE: t3/pkg_b/__init__.py    (tied with pkg_a/__init__.py)
✗ DELETE: t3/vendor/lib/LICENSE   (tied with pkg_a/LICENSE)

Both are structurally required files, and the loser is picked by path order rather than by evidence that it is a copy. Recursion turns this from an edge case into the common case, so #7 should be settled first or in the same PR.

Cross-directory duplicates also want their own tie-break rule once #7 defines one — prefer the shallower path, or decline to recommend across directories at all.

Remaining smaller flags

flag	purpose
--version	version string, built from ldflags
--min-size N	ignore files below N bytes (interacts with #6)
--exclude PATTERN	skip matching names; needed by -r above

Tests to write first

• -r finds duplicates across subdirectories; without it, subdirectories are untouched (there is already a TestScanSkipsSubdirectories guarding the default).
• Excluded directories are not descended into — assert on a fixture containing a .git directory.
• A path that begins with - is still handled, via --.
• Cross-directory ties behave per whatever Equal-priority ties still nominate a file for deletion with no evidence it is a copy #7 decides.