chore: lint and format entire codebase

Run ruff check --fix: remove unused imports (F401), fix f-strings
without placeholders (F541), remove unused variables (F841), fix
duplicate dict key (F601).

Run isort --profile black: normalize import ordering across all files.

Run ruff format: apply consistent formatting (black-compatible) to
all 58 Python files.

3 intentional E402 remain (imports after require_yaml() must execute
after yaml is available).

scripts/exporter/systemdat_exporter.py

@@ -58,16 +58,18 @@ class Exporter(BaseExporter):
         ]
         if version:
             lines.append(f"\tversion {version}")
-        lines.extend([
-            '\tauthor "libretro"',
-            '\thomepage "https://github.com/libretro/libretro-database/blob/master/dat/System.dat"',
-            '\turl "https://raw.githubusercontent.com/libretro/libretro-database/master/dat/System.dat"',
-            ")",
-            "",
-            "game (",
-            '\tname "System"',
-            '\tcomment "System"',
-        ])
+        lines.extend(
+            [
+                '\tauthor "libretro"',
+                '\thomepage "https://github.com/libretro/libretro-database/blob/master/dat/System.dat"',
+                '\turl "https://raw.githubusercontent.com/libretro/libretro-database/master/dat/System.dat"',
+                ")",
+                "",
+                "game (",
+                '\tname "System"',
+                '\tcomment "System"',
+            ]
+        )
 
         systems = truth_data.get("systems", {})
         for sys_id in sorted(systems):