standardize packaging, tooling, docs, CI, and licensing

mail_intake/config.py

@@ -12,7 +12,6 @@ environment reads to ensure predictability and testability.
 """
 
 from dataclasses import dataclass
-from typing import Optional
 
 
 @dataclass(frozen=True)
@@ -46,12 +45,12 @@ class MailIntakeConfig:
     Whether ingestion should operate in read-only mode.
     """
 
-    credentials_path: Optional[str] = None
+    credentials_path: str | None = None
     """
     Optional path to provider credentials configuration.
     """
 
-    token_path: Optional[str] = None
+    token_path: str | None = None
     """
     Optional path to persisted authentication tokens.
     """