fix: parse meta.initialBlur field that was silently ignored

The initialBlur field is defined in DemoMeta, documented in README,
present in schema.json, and consumed by the generator — but validateDemoMeta
in parser.ts never read or forwarded it. Any YAML using `initialBlur`
had the value silently dropped, so the generator always fell back to
the default blur of 1px regardless of what was configured.

Co-authored-by: HarshSheth1128 <harshsheth1128@users.noreply.github.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

src/parser.ts

@@ -130,6 +130,13 @@ function validateDemoMeta(raw: unknown, filePath?: string): DemoMeta {
     result.speed = validateSpeedConfig(meta.speed, filePath);
   }
 
+  if (meta.initialBlur !== undefined) {
+    if (typeof meta.initialBlur !== 'number' || !Number.isFinite(meta.initialBlur) || meta.initialBlur < 0) {
+      throw new ParseError('meta.initialBlur must be a non-negative number', filePath);
+    }
+    result.initialBlur = meta.initialBlur;
+  }
+
   return result;
 }