fix: replace deprecated datetime.utcnow() with timezone-aware alternatives

Replace all datetime.utcnow() calls with datetime.now(timezone.utc) to fix Python 3.13 deprecation warnings:

- Update SQLAlchemy model defaults in project.py with lambda functions
- Fix JWT token generation in auth providers
- Update test fixtures with timezone-aware datetime
- Add timezone imports where needed

Fixes Python 3.13 deprecation warnings that appeared when running commands like 'bm project add'.
Code is now ready for Python 3.15 when datetime.utcnow() will be removed.

Fixes #210

Co-authored-by: Drew Cain <groksrc@users.noreply.github.com>

tests/mcp/test_auth_provider.py

@@ -1,7 +1,7 @@
 """Tests for OAuth authentication provider."""
 
 import pytest
-from datetime import datetime, timedelta
+from datetime import datetime, timedelta, timezone
 from mcp.server.auth.provider import AuthorizationParams
 from mcp.shared.auth import OAuthClientInformationFull
 from pydantic import AnyHttpUrl
@@ -185,7 +185,7 @@ class TestBasicMemoryOAuthProvider:
             token=token_str,
             client_id=client.client_id,
             scopes=["read", "write"],
-            expires_at=int((datetime.utcnow() + timedelta(hours=1)).timestamp()),
+            expires_at=int((datetime.now(timezone.utc) + timedelta(hours=1)).timestamp()),
         )
         provider.access_tokens[token_str] = access_token
 
@@ -226,7 +226,7 @@ class TestBasicMemoryOAuthProvider:
         provider.authorization_codes[auth_code] = BasicMemoryAuthorizationCode(
             code=auth_code,
             scopes=["read"],
-            expires_at=(datetime.utcnow() - timedelta(minutes=1)).timestamp(),
+            expires_at=(datetime.now(timezone.utc) - timedelta(minutes=1)).timestamp(),
             client_id=client.client_id,
             code_challenge="challenge",
             redirect_uri=AnyHttpUrl("http://localhost:3000/callback"),
@@ -288,7 +288,7 @@ class TestBasicMemoryOAuthProvider:
             token=expired_token_str,
             client_id="test-client",
             scopes=["read"],
-            expires_at=int((datetime.utcnow() - timedelta(minutes=1)).timestamp()),  # Expired
+            expires_at=int((datetime.now(timezone.utc) - timedelta(minutes=1)).timestamp()),  # Expired
         )
         provider.access_tokens[expired_token_str] = expired_access_token