fix(core): separate info count from warning count in linter results

The linter was computing warningCount as findings.length - errorCount,
which lumped info-severity findings into the warning count. Now counts
warnings and infos separately, and adds a new infoCount field.

Reproducer:
  # Create composition with timed element missing class="clip"
  npx hyperframes lint        # Was: "0 errors, 1 warning(s)"
  npx hyperframes lint --json # Was: severity: "info" but warningCount: 1
  # Now warningCount: 0, infoCount: 1

packages/core/src/lint/hyperframeLinter.ts

@@ -636,12 +636,14 @@ export function lintHyperframeHtml(
   }
 
   const errorCount = findings.filter((finding) => finding.severity === "error").length;
-  const warningCount = findings.length - errorCount;
+  const warningCount = findings.filter((finding) => finding.severity === "warning").length;
+  const infoCount = findings.filter((finding) => finding.severity === "info").length;
 
   return {
     ok: errorCount === 0,
     errorCount,
     warningCount,
+    infoCount,
     findings,
   };
 }

packages/core/src/lint/types.ts

@@ -15,6 +15,7 @@ export type HyperframeLintResult = {
   ok: boolean;
   errorCount: number;
   warningCount: number;
+  infoCount: number;
   findings: HyperframeLintFinding[];
 };