feat: skip a verified placeholder file in The Only Doe 0.05 instead of failing the media conversion

gui/journal_icon.png in that build is a text note ("PLACEHOLDER: Download a journal icon...") with an
.svg next to it, so Ren'Py cannot load it either. A build can now list placeholder files by path and
SHA-256; only an exact match is skipped and the report carries a non-blocking warning. The full
conversion of the game (2898 files, 2.77 GB) now finishes without failed media.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

backend/tests/test_game_profiles.py

@@ -71,3 +71,15 @@ def test_known_build_line_patch_requires_the_exact_line():
     assert renpy_builds.prepare_source("renpy/the-only-doe-0.05", "other.rpy", source) == source
     edited = source.replace("spitroast", "other")
     assert renpy_builds.prepare_source("renpy/the-only-doe-0.05", "sleep.rpy", edited) == edited
+
+
+def test_placeholder_media_is_skipped_only_on_an_exact_match(tmp_path):
+    from app.games import renpy_builds
+
+    icon = tmp_path / "gui" / "journal_icon.png"
+    icon.parent.mkdir()
+    icon.write_text("PLACEHOLDER: Download a journal icon from a free resource and save as journal_icon.png in gui folder.")
+    assert renpy_builds.placeholder_files("renpy/the-only-doe-0.05", tmp_path) == {icon}
+    assert renpy_builds.placeholder_files(None, tmp_path) == set()
+    icon.write_text("a real file now")
+    assert renpy_builds.placeholder_files("renpy/the-only-doe-0.05", tmp_path) == set()