⬆️ Upgrade devDependencies to latest major versions

- @types/node 22.20.1 -> 26.4.1
- c8 10.1.3 -> 12.0.0
- check-outdated 2.16.1 -> 3.0.0
- cspell 8.19.4 -> 10.2.1
- lefthook 1.13.6 -> 2.1.12
- sort-package-json 3.7.1 -> 4.0.0
- type-fest 4.41.0 -> 5.9.0

Verified all configs remain compatible without changes:
- cspell 10 reads the existing JSON config (v0.2 format unchanged)
- lefthook 2 accepts the v1-style config (pre-commit.jobs[], commands:)
- c8 12 still wraps 'node --test --strip-types' and produces the same
  text/lcov/html reports
- check-outdated 3 keeps the --ignore-packages and --ignore-pre-releases
  flags we use

Full pipeline passes:
- npm run check exits 0 (oxlint, oxfmt, tsc, cspell, sort-package-json,
  check-outdated all green)
- npm test: 6/6 pass
- npm run test:ci: coverage report generated successfully
- lefthook run pre-commit: hooks execute correctly

package.json

@@ -49,17 +49,17 @@
         "use:git-commit-message": "cp commit-message-template .git/COMMIT_EDITMSG || true"
     },
     "devDependencies": {
-        "@types/node": "^22.10.0",
-        "c8": "^10.1.3",
-        "check-outdated": "^2.13.0",
-        "cspell": "^8.19.3",
+        "@types/node": "^26.4.1",
+        "c8": "^12.0.0",
+        "check-outdated": "^3.0.0",
+        "cspell": "^10.2.1",
         "expect-type": "1.4.0",
-        "lefthook": "^1.11.12",
+        "lefthook": "^2.1.12",
         "oxfmt": "^0.66.0",
         "oxlint": "^1.81.0",
-        "sort-package-json": "^3.1.0",
+        "sort-package-json": "^4.0.0",
         "tslib": "^2.8.1",
-        "type-fest": "^4.40.1",
+        "type-fest": "^5.9.0",
         "typescript": "^7.0.2"
     },
     "optionalDependencies": {