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, 5 insertions, 7 deletions

diff --git a/packages/meshbay-node/src/meshbay_node/roster.py b/packages/meshbay-node/src/meshbay_node/roster.py
index 8c9b3ef..9478a32 100644
--- a/packages/meshbay-node/src/meshbay_node/roster.py
+++ b/packages/meshbay-node/src/meshbay_node/roster.py
@@ -24,13 +24,11 @@ from __future__ import annotations
 import hashlib
 import json
 import logging
-import os
 import secrets
-from datetime import datetime, timedelta, timezone
+from datetime import UTC, datetime, timedelta
 from pathlib import Path
 
 import aiosqlite
-
 from meshbay_common.paths import fold
 
 log = logging.getLogger(__name__)
@@ -194,11 +192,11 @@ def hash_code(code: str) -> str:
 
 
 def _now() -> str:
-    return datetime.now(timezone.utc).isoformat(timespec="seconds")
+    return datetime.now(UTC).isoformat(timespec="seconds")
 
 
 def _iso_in(seconds: int) -> str:
-    return (datetime.now(timezone.utc)
+    return (datetime.now(UTC)
             + timedelta(seconds=seconds)).isoformat(timespec="seconds")
 
 
@@ -1073,7 +1071,7 @@ class Roster:
             (group_id, user_id),
         )
         code = generate_code()
-        expires = datetime.now(timezone.utc) + timedelta(seconds=ttl)
+        expires = datetime.now(UTC) + timedelta(seconds=ttl)
         await self._db.execute(
             "INSERT INTO invites (code_hash, group_id, user_id, username, role, "
             "created_by, created_at, expires_at) VALUES (?, ?, ?, ?, ?, ?, ?, ?)",
@@ -1106,7 +1104,7 @@ class Roster:
         # redeemed by whoever finds it first.
         if invite["user_id"] != user_id:
             return None
-        if datetime.fromisoformat(invite["expires_at"]) < datetime.now(timezone.utc):
+        if datetime.fromisoformat(invite["expires_at"]) < datetime.now(UTC):
             return None
 
         cur = await self._db.execute(