chore: drop legacy eslint/prettier configs; restrict PR workflow permissions

- Remove .editorconfig, .eslintignore, .eslintrc.cjs, .prettierignore
  (lint/format handled by oxlint + oxfmt).
- pr.yml: add `permissions: contents: read` for least-privilege.

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

Author: maxholman

.editorconfig

@@ -4,6 +4,9 @@ on:
   pull_request:
     branches: ["canary", "master"]
 
+permissions:
+  contents: read
+
 jobs:
   test:
     strategy: