chore(release): 0.0.3

Squash-merge lib-standardisation: adopt repo standards across packaging,
tooling, docs, and CI.

- standardize pyproject.toml (canonical packaging, lint config, extras, GSDFC pydoclint)
- add py.typed marker, modernize type hints and Google-style docstrings
- nest generated docs under docs/lib and docs/mcp; add hand-written wiki
- adopt standard Type A PyPI CI pipeline (tag==version guard + quality gate)
- promote generated CHANGELOG.md; bump version to 0.0.3

mail_intake/credentials/pickle.py

@@ -16,7 +16,7 @@ untrusted environments.
 """
 
 import pickle
-from typing import Optional, TypeVar
+from typing import TypeVar
 
 from mail_intake.credentials.store import CredentialStore
 
@@ -55,12 +55,12 @@ class PickleCredentialStore(CredentialStore[T]):
         """
         self.path = path
 
-    def load(self) -> Optional[T]:
+    def load(self) -> T | None:
         """
         Load credentials from the local filesystem.
 
         Returns:
-            Optional[T]:
+            T | None:
                 An instance of type `T` if credentials are present and
                 successfully deserialized; otherwise `None`.