refactor: DRY consolidation + 83 unit tests

Moved shared functions to common.py (single source of truth):
- check_inside_zip (was in verify.py, imported by generate_pack)
- build_zip_contents_index (was duplicated in verify + generate_pack)
- load_emulator_profiles (was in verify, cross_reference, generate_site)
- group_identical_platforms (was in verify + generate_pack)

Added tests/ with 83 unit tests covering:
- resolve_local_file: SHA1, MD5, name, alias, truncated, zip_contents
- verify: existence, md5, zipped_file, multi-hash, severity mapping
- aliases: field parsing, by_name indexing, beetle_psx field rename
- pack: dedup, file_status, zipped_file inner check, EmuDeck entries
- severity: all 12 combinations, platform-native behavior

0 regressions: pipeline.py --all produces identical results.

scripts/cross_reference.py

@@ -25,27 +25,13 @@ except ImportError:
     sys.exit(1)
 
 sys.path.insert(0, os.path.dirname(__file__))
-from common import load_database, load_platform_config
+from common import load_database, load_emulator_profiles, load_platform_config
 
 DEFAULT_EMULATORS_DIR = "emulators"
 DEFAULT_PLATFORMS_DIR = "platforms"
 DEFAULT_DB = "database.json"
 
 
-def load_emulator_profiles(emulators_dir: str) -> dict[str, dict]:
-    """Load all emulator YAML profiles."""
-    profiles = {}
-    emu_path = Path(emulators_dir)
-    if not emu_path.exists():
-        return profiles
-    for f in sorted(emu_path.glob("*.yml")):
-        with open(f) as fh:
-            profile = yaml.safe_load(fh) or {}
-        if "emulator" in profile:
-            profiles[f.stem] = profile
-    return profiles
-
-
 def load_platform_files(platforms_dir: str) -> tuple[dict[str, set[str]], dict[str, set[str]]]:
     """Load all platform configs and collect declared filenames + data_directories per system."""
     declared = {}