feat(auth): implement JWT TTL and expiration

added access_token_ttl setting
fixed public and private key mismatch while decoding jwt
decode_jwt now returns None on expired tokens instead of raising exc
generate_pair converts sub to string and uses dynamic expiration

config.py

@@ -16,6 +16,8 @@ class Settings(BaseSettings):
     private_key_fp: str = Field()
     public_key_fp: str = Field()
 
+    access_token_ttl: int = Field(description="Access token TTL (minutes)")
+
     @computed_field
     @property
     def db_url(self) -> str: