chore(deps): update PyJWT to 2.15.1 across samples

Bump PyJWT to 2.15.1 to resolve Dependabot security alerts:
- appengine/standard/firebase/firenotes/backend/requirements.txt: update pyjwt from 1.7.1 to 2.15.1 (python_version >= '3.10')
- iap/requirements.txt: pin PyJWT to 2.15.1
- run/mcp-server/uv.lock: upgrade transitive pyjwt lock from 2.13.0 to 2.15.1 and normalize registry URLs to PyPI

Author: XrossFox

appengine/standard/firebase/firenotes/backend/requirements.txt

@@ -1,5 +1,5 @@
 Flask==3.1.3; python_version >= '3.9'
-pyjwt==1.7.1; python_version < '3.0'
+pyjwt==2.15.1; python_version >= '3.10'
 flask-cors==6.0.0
 google-auth==2.17.3; python_version < '3.0'
 google-auth==2.17.3; python_version > '3.0'

iap/requirements.txt

@@ -6,4 +6,4 @@ requests==2.34.2
 requests-toolbelt==1.0.0
 Werkzeug==3.1.8; python_version >= '3.9'
 google-cloud-iam~=2.17.0
-PyJWT~=2.10.1
+PyJWT==2.15.1