fix(cli): respect --json flag on lint error paths

When lint encountered an error (e.g., invalid directory), it output
plain text even with --json, breaking JSON parsing pipelines for
agents. Now wraps the entire lint command in try-catch that emits
JSON errors when --json is set.

Reproducer:
  npx hyperframes lint --json /nonexistent/path
  # Was: plain text "Not a directory: /nonexistent/path"
  # Now: {"ok": false, "error": "Not a directory: /nonexistent/path", ...}

packages/cli/src/commands/lint.ts

@@ -15,6 +15,7 @@ export default defineCommand({
     json: { type: "boolean", description: "Output findings as JSON", default: false },
   },
   async run({ args }) {
+    try {
       const project = resolveProject(args.dir);
       const htmlFiles = walkDir(project.dir).filter((f) => f.endsWith(".html"));
 
@@ -73,5 +74,27 @@ export default defineCommand({
       const summaryIcon = totalErrors > 0 ? c.error("◇") : c.success("◇");
       console.log(`\n${summaryIcon}  ${totalErrors} error(s), ${totalWarnings} warning(s)`);
       process.exit(totalErrors > 0 ? 1 : 0);
+    } catch (err: unknown) {
+      const message = err instanceof Error ? err.message : String(err);
+      if (args.json) {
+        console.log(
+          JSON.stringify(
+            withMeta({
+              ok: false,
+              error: message,
+              findings: [],
+              errorCount: 0,
+              warningCount: 0,
+              filesScanned: 0,
+            }),
+            null,
+            2,
+          ),
+        );
+        process.exit(1);
+      }
+      console.error(message);
+      process.exit(1);
+    }
   },
 });