fix: mock-forgejo path parsing bug + non-fatal cron in smoke-init (#586)

- Fix off-by-one in mock admin/users/{username}/repos path extraction
  (parts[4] was 'users', not the username — should be parts[5])
- Change _install_cron_impl to return 1 instead of exit 1 when crontab
  is missing, so cron failure doesn't abort entire init

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/mock-forgejo.py

@@ -505,8 +505,9 @@ class ForgejoHandler(BaseHTTPRequestHandler):
         require_token(self)
 
         parts = self.path.split("/")
-        if len(parts) >= 6:
-            target_user = parts[4]
+        # /api/v1/admin/users/{username}/repos → parts[5] is the username
+        if len(parts) >= 7:
+            target_user = parts[5]
         else:
             json_response(self, 400, {"message": "username required"})
             return