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.pyi

@@ -1,4 +1,5 @@
-from typing import Optional, TypeVar
+from typing import TypeVar
+
 from .store import CredentialStore
 
 T = TypeVar("T")
@@ -6,6 +7,6 @@ T = TypeVar("T")
 class PickleCredentialStore(CredentialStore[T]):
     path: str
     def __init__(self, path: str) -> None: ...
-    def load(self) -> Optional[T]: ...
+    def load(self) -> T | None: ...
     def save(self, credentials: T) -> None: ...
     def clear(self) -> None: ...