style: say which lint rules this repo keeps, then keep them

`[tool.ruff]` set a line length and a target version and nothing else, so which
rules ran depended on the installed ruff's defaults — fine while nobody ran it,
not fine for a CI job that can turn a push red because a tool changed its mind.

The set is named explicitly (E, F, I, UP, SIM, B, RUF) with three ignores that
are each a real decision rather than a shrug: B008, because FastAPI's whole
dependency idiom is a call in a default argument; E501, because wrapping prose
is a formatter's business; and RUF001, because the reports and the bot speak
Russian and "ambiguous character" is the wrong complaint about a string the
user is meant to read.

The 73 findings that remained are fixed — mostly `datetime.timezone.utc` →
`datetime.UTC`, `typing.Callable` → `collections.abc.Callable`, import order,
and unused `noqa` markers — plus seven by hand: `contextlib.suppress` for two
try/except/pass pairs, unpacking instead of list concatenation, one negated
return.

`ruff format` is deliberately *not* adopted: it would reformat 51 files, and
some of the layout here is hand-set (the comment tables, the DNS wire-format
structs) in ways a formatter flattens.

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

backend/app/sources/base.py

@@ -51,7 +51,7 @@ class SourceResult:
     error: str | None = None
 
     @classmethod
-    def failed(cls, source: str, error: str) -> "SourceResult":
+    def failed(cls, source: str, error: str) -> SourceResult:
         return cls(source=source, items=[], ok=False, error=error)
 
 

backend/app/sources/google_tasks.py

@@ -11,8 +11,9 @@ still things you can spend a pomodoro on.
 
 from __future__ import annotations
 
+from collections.abc import Iterator
 from datetime import date
-from typing import Any, Iterator
+from typing import Any
 
 import httpx
 

backend/app/sources/jira.py

@@ -13,8 +13,9 @@ notices it has left the "open issues" query. One owner per task.
 from __future__ import annotations
 
 import re
+from collections.abc import Iterator
 from datetime import date
-from typing import Any, Iterator
+from typing import Any
 
 import httpx
 

backend/app/sources/registry.py

@@ -8,8 +8,9 @@ empty task list.
 from __future__ import annotations
 
 import logging
+from collections.abc import Callable
 from concurrent.futures import ThreadPoolExecutor
-from typing import Any, Callable
+from typing import Any
 
 from app.settings_schema import AppSettings
 from app.sources.base import SourceError, SourceResult, TodoItem

backend/app/sources/todoist.py

@@ -9,8 +9,9 @@ for people who want the narrower list.
 
 from __future__ import annotations
 
+from collections.abc import Iterator
 from datetime import date
-from typing import Any, Iterator
+from typing import Any
 
 import httpx