Fix extractRegion() matching region names that are substrings of others

The `extractRegion()` function in `sync-snippets.ts` used `indexOf()` to
find region markers like `//#region persistData`. This caused incorrect
matching when one region name was a prefix of another—searching for
`persistData` would match `//#region persistDataServer` first if it
appeared earlier in the file.

The fix detects the file's line ending style and appends it to region
markers, ensuring exact matches:
- `//#region persistData\n` no longer matches `//#region persistDataServer\n`

This corrects `docs/patterns.md` where the `persistData` code fence was
incorrectly showing server-side code instead of client-side localStorage
helpers.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

scripts/sync-snippets.ts

@@ -254,8 +254,9 @@ function extractRegion(
     );
   }
 
-  const regionStart = `//#region ${regionName}`;
-  const regionEnd = `//#endregion ${regionName}`;
+  const lineEnding = exampleContent.includes("\r\n") ? "\r\n" : "\n";
+  const regionStart = `//#region ${regionName}${lineEnding}`;
+  const regionEnd = `//#endregion ${regionName}${lineEnding}`;
 
   const startIndex = exampleContent.indexOf(regionStart);
   if (startIndex === -1) {