style: adopt ruff (format + lint) at 88, replacing black/isort/flake8

Format-only: Python files are AST-identical apart from import order.
pre-commit end-of-file/trailing-whitespace fixes applied repo-wide.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

.pre-commit-config.yaml

@@ -1,6 +1,6 @@
 repos:
 -   repo: https://github.com/pre-commit/pre-commit-hooks
-    rev: v4.5.0
+    rev: v6.0.0
     hooks:
     -   id: check-yaml
     -   id: check-added-large-files
@@ -9,23 +9,10 @@ repos:
     -   id: end-of-file-fixer
     -   id: trailing-whitespace
 
-# isort -- sorts imports
--   repo: https://github.com/timothycrosley/isort
-    rev: 5.13.2
+# ruff replaces black, isort and flake8. Keep rev equal to the ruff pin in pyproject.toml.
+-   repo: https://github.com/astral-sh/ruff-pre-commit
+    rev: v0.16.10
     hooks:
-    -   id: isort
-        args: ["--profile", "black", "--filter-files"]
-
-# Flake8
--   repo: https://github.com/pycqa/flake8
-    rev: '7.0.0'
-    hooks:
-    -   id: flake8
-
-# Black
-# Using this mirror lets us use mypyc-compiled black, which is about 2x faster
-- repo: https://github.com/psf/black-pre-commit-mirror
-  rev: 24.2.0
-  hooks:
-    - id: black
-      language_version: python3.8
+    -   id: ruff-check
+        args: [--fix]
+    -   id: ruff-format