Fix wallpaper upgrade compatibility and Settings icon clipping

Allow installed releases to omit the two newer appearance wallpapers while keeping new bundle verification strict. Fit the Settings header symbol within its square slot without clipping.

Verified 30 installer tests, the real upgrade dry-run, and release rendering previews on GPU and software backends.

scripts/installer/install.py

@@ -125,7 +125,7 @@ def record(rule, name=None):
             for key, value in rule.items() if key != 'source'}
 
 
-def validate_bundle(bundle):
+def validate_bundle(bundle, *, installed=False):
     if bundle.is_symlink() or not bundle.is_dir():
         fail(f'Bundle must be a directory, not a symlink: {bundle}')
 
@@ -162,7 +162,14 @@ def validate_bundle(bundle):
         seen.add(target)
 
     actual = {str(path.relative_to(bundle)) for path in bundle.rglob('*') if path.is_file()}
-    if not expected.keys() <= seen or actual != seen | {'manifest.json'}:
+    required = expected.keys()
+    if installed:
+        # Installed releases may predate the appearance-specific wallpapers.
+        # New bundles must include them; upgrades and rollback verify the older
+        # release's recorded files without requiring these later additions.
+        required = required - {'wallpapers/ferese-wallpaper-dark.jpg', 'wallpapers/ferese-wallpaper-light.png'}
+
+    if not required <= seen or actual != seen | {'manifest.json'}:
         fail('Bundle is incomplete or contains unlisted files')
 
     return manifest
@@ -277,7 +284,7 @@ class Installation:
         if not (directory / 'manifest.json').is_file():
             fail(f'Release {release} predates verified bundles; select a bundled release for rollback')
 
-        return validate_bundle(directory)
+        return validate_bundle(directory, installed=True)
 
     def current_publication(self, current):
         if not current: