fix(prd-1): fix CI test failures and Forgejo permission check

Two issues found during M8 E2E testing on Forgejo:

1. CI test failures (31 tests): Unit tests assume GitHub context but
   Forgejo runner sets GITHUB_SERVER_URL=git.wxs.ro, causing
   detectPlatform() to return "forgejo" and module-level constants in
   config.ts to use Forgejo URLs. Fixed by setting GITHUB_SERVER_URL
   in the test step env. Forgejo-specific tests already override with
   PLATFORM=forgejo in their beforeEach.

2. Permission check 403: Forgejo's getCollaboratorPermissionLevel
   requires admin access. Added checkForgejoPermissions() that uses
   GET /repos/{owner}/{repo} instead — returns a permissions object
   with { admin, push, pull } booleans for the authenticated token.

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

.forgejo/workflows/ci.yml

@@ -36,6 +36,12 @@ jobs:
 
       - name: Run tests
         run: bun test
+        env:
+          # Unit tests assume GitHub context. Override Forgejo runner's
+          # GITHUB_SERVER_URL so module-level constants (config.ts) and
+          # detectPlatform() default to GitHub. Forgejo-specific tests
+          # explicitly set PLATFORM=forgejo in their own beforeEach.
+          GITHUB_SERVER_URL: https://github.com
 
   prettier:
     runs-on: grunt