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/models/thread.py

@@ -12,7 +12,6 @@ for higher-level correspondence workflows.
 
 from dataclasses import dataclass, field
 from datetime import datetime
-from typing import List, Set
 
 from mail_intake.models.message import MailIntakeMessage
 
@@ -42,12 +41,12 @@ class MailIntakeThread:
     Normalized subject line used to group related messages.
     """
 
-    participants: Set[str] = field(default_factory=set)
+    participants: set[str] = field(default_factory=set)
     """
     Set of unique participant email addresses observed in the thread.
     """
 
-    messages: List[MailIntakeMessage] = field(default_factory=list)
+    messages: list[MailIntakeMessage] = field(default_factory=list)
     """
     Ordered list of messages belonging to this thread.
     """