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/exceptions.py

@@ -1,10 +1,8 @@
 """
+# Summary
+
 Exception hierarchy for Mail Intake.
 
----
-
-## Summary
-
 This module defines the **canonical exception types** used throughout the
 Mail Intake library.