chore: anonymize internal URLs for public release

Replace git.wxs.ro with forgejo.example.com in tests and docs.
Add public repo guidelines to CLAUDE.md.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

test/platform-detector.test.ts

@@ -75,7 +75,7 @@ describe("detectPlatform", () => {
 
   describe("GITHUB_SERVER_URL heuristic", () => {
     it("should return 'forgejo' for non-github.com server URLs", () => {
-      process.env.GITHUB_SERVER_URL = "https://git.wxs.ro";
+      process.env.GITHUB_SERVER_URL = "https://forgejo.example.com";
       expect(detectPlatform()).toBe("forgejo");
     });