style: ruff's own fixes, mechanically applied

`ruff check .` had gone unrun long enough to report 568 errors, which is the
same as having no linter: the next real finding would have been invisible in the
noise. This is the 521 it fixes by itself, in 173 files, and nothing else — the
98 it cannot fix are the next commit.

What actually changed: import sorting (225), imports nobody used (87, none of
them a re-export — no `__init__.py` is touched, which was the one way this could
have broken an import elsewhere), `datetime.timezone.utc` to `datetime.UTC` (69)
and `asyncio.TimeoutError` to `TimeoutError` (18), both plain aliases on the 3.12
this project requires, `Optional[X]` to `X | None` (24), and f-strings with
nothing to interpolate (19).

Checked rather than assumed: every module in the three packages still imports,
and the suite is 2893 passed — the same count, test for test, as the merge
before it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

1 files changed, 10 insertions, 4 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/db/models.py b/packages/meshbay-hub/src/meshbay_hub/db/models.py
index 62e4a11..38c4723 100644
--- a/packages/meshbay-hub/src/meshbay_hub/db/models.py
+++ b/packages/meshbay-hub/src/meshbay_hub/db/models.py
@@ -11,17 +11,23 @@ Tables:
 """
 
 import uuid
-from datetime import datetime, timezone
+from datetime import UTC, datetime
 
 from sqlalchemy import (
-    Boolean, DateTime, ForeignKey, Index, Integer,
-    String, Text, UniqueConstraint, text,
+    Boolean,
+    DateTime,
+    ForeignKey,
+    Index,
+    Integer,
+    String,
+    Text,
+    text,
 )
 from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column, relationship
 
 
 def _now() -> datetime:
-    return datetime.now(timezone.utc)
+    return datetime.now(UTC)
 
 def _uuid() -> str:
     return str(uuid.uuid4())