fix: report renames honestly in a dry run

--dry-run described a FAT32 rename as an encode. process() skipped the rename
whenever dry_run was set, then found no file at the target and fell through to
the encode path, so a preview of enabling --fat32-safe announced a full
re-encode of every track whose name held a reserved character. The real run
moves those files in a moment. A preview that inverts the cost of the thing
being previewed is worse than no preview at all.

Prune compounded it. With nothing renamed, the pre-sanitisation files are still
on disk, and they were reported as orphans due for deletion -- so the same dry
run claimed the library would be re-encoded and the originals thrown away,
neither of which is true.

Renames are now their own outcome: reported as "would rename" in a dry run,
counted separately from encodes in the pass summary, and excluded from the
orphan list when a dry run leaves them in place.

tests/test_music_mirror.py

@@ -558,3 +558,58 @@ def test_a_cover_left_without_tracks_is_pruned(tmp_path, make_flac, make_cover):
     run(source, mirror)
 
     assert not (mirror / "Gone").exists()
+
+
+def test_a_dry_run_reports_a_rename_not_an_encode(tmp_path, make_flac, caplog):
+    """The difference between moving a file and re-encoding it is the
+    difference between a minute and an afternoon, so a dry run must not
+    describe the first as the second."""
+    source = tmp_path / "src"
+    mirror = tmp_path / "dst"
+    make_flac(source / "Album" / "Where Are You?.flac")
+    run(source, mirror)
+
+    with caplog.at_level("INFO"):
+        run(source, mirror, "--fat32-safe", "--dry-run")
+
+    assert "would rename" in caplog.text
+    assert "would encode" not in caplog.text
+
+
+def test_a_dry_run_does_not_call_the_old_paths_orphans(tmp_path, make_flac, caplog):
+    """Nothing was renamed, so they are still there -- but they are the files a
+    real run would move, not files it would delete."""
+    source = tmp_path / "src"
+    mirror = tmp_path / "dst"
+    make_flac(source / "Album" / "Where Are You?.flac")
+    run(source, mirror)
+
+    with caplog.at_level("INFO"):
+        run(source, mirror, "--fat32-safe", "--dry-run")
+
+    assert "would remove orphan" not in caplog.text
+
+
+def test_a_dry_run_moves_nothing(tmp_path, make_flac):
+    source = tmp_path / "src"
+    mirror = tmp_path / "dst"
+    make_flac(source / "Album" / "Where Are You?.flac")
+    run(source, mirror)
+
+    run(source, mirror, "--fat32-safe", "--dry-run")
+
+    assert (mirror / "Album" / "Where Are You?.mp3").is_file()
+    assert not (mirror / "Album" / "Where Are You_.mp3").exists()
+
+
+def test_renames_are_counted_separately_from_encodes(tmp_path, make_flac, caplog):
+    source = tmp_path / "src"
+    mirror = tmp_path / "dst"
+    make_flac(source / "Album" / "Where Are You?.flac")
+    run(source, mirror)
+
+    with caplog.at_level("INFO"):
+        run(source, mirror, "--fat32-safe")
+
+    assert "1 renamed" in caplog.text
+    assert "0 encoded" in caplog.text