ci: transition pre-commit to prek with built-in hooks

Switch the hook runner from pre-commit to prek (the Rust reimplementation) and
adopt prek's native built-in hooks.

- CI: replace the setup-uv + cache + `uvx pre-commit run` steps with the
  j178/prek-action action (installs prek and caches hook environments). The
  workflow is renamed to prek.yaml with job `prek`; SKIP=no-commit-to-branch,mypy
  is preserved (mypy has its own workflow; no-commit-to-branch is procedural).
- Config: replace the pre-commit/pre-commit-hooks repo (rev v6.0.0) with prek's
  `repo: builtin`. All hooks in use have built-in equivalents; also enable
  check-toml, check-case-conflict, fix-byte-order-marker, and
  check-illegal-windows-names.
- README: install hooks via `uvx prek install --overwrite ...`.

prek reads the same .pre-commit-config.yaml, and renovate's pre-commit manager
continues to track the remaining external hook revisions.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: bakerkj

.github/workflows/pre-commit.yaml

@@ -0,0 +1,19 @@
+name: prek
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+jobs:
+  prek:
+    runs-on: ubuntu-24.04
+    steps:
+      - uses: actions/checkout@v6.0.2
+      # mypy is skipped here (the dedicated mypy.yaml workflow runs it with a
+      # full HA dependency env).
+      - uses: j178/prek-action@v2.0.4
+        env:
+          SKIP: no-commit-to-branch,mypy
+        with:
+          extra-args: --all-files

.github/workflows/prek.yaml

@@ -1,15 +1,18 @@
 repos:
-  - repo: https://github.com/pre-commit/pre-commit-hooks
-    rev: v6.0.0
+  - repo: builtin
     hooks:
       - id: no-commit-to-branch
         args: ["--branch", "main"]
       - id: trailing-whitespace
       - id: end-of-file-fixer
+      - id: fix-byte-order-marker
       - id: check-yaml
       - id: check-json
+      - id: check-toml
       - id: check-added-large-files
       - id: check-merge-conflict
+      - id: check-case-conflict
+      - id: check-illegal-windows-names
       - id: detect-private-key
       - id: check-executables-have-shebangs
       - id: check-shebang-scripts-are-executable

.pre-commit-config.yaml

@@ -40,11 +40,11 @@ Commits must follow the
 release-please uses commit prefixes (`feat:`, `fix:`, etc.) to drive version
 bumps.
 
-After cloning, install the pre-commit hooks **including the commit-msg hook**
-(the default `pre-commit install` only wires up pre-commit-stage hooks):
+After cloning, install the hooks **including the commit-msg hook** (the default
+`prek install` only wires up pre-commit-stage hooks):
 
 ```
-uvx pre-commit install --hook-type pre-commit --hook-type commit-msg
+uvx prek install --overwrite --hook-type pre-commit --hook-type commit-msg
 ```
 
 Without `--hook-type commit-msg`, malformed commit messages won't be caught