Add commit message normalizer hook and install script

- scripts/normalize-commit-msg.js: capitalizes subject, strips trailing
  period, trims whitespace, warns when subject > 72 chars
- scripts/commit-msg: shell wrapper symlinked into .git/hooks/commit-msg
- scripts/install-hooks.sh: contributor setup script (sh scripts/install-hooks.sh)
- scripts/package.json: test runner + hooks:install npm script
- scripts/__tests__/normalize-commit-msg.test.js: 15 unit tests

Nightshift-Task: commit-normalize
Nightshift-Ref: https://github.com/marcus/nightshift

scripts/package.json

@@ -0,0 +1,12 @@
+{
+  "name": "budget-scripts",
+  "version": "1.0.0",
+  "scripts": {
+    "test": "vitest run",
+    "test:watch": "vitest",
+    "hooks:install": "sh install-hooks.sh"
+  },
+  "devDependencies": {
+    "vitest": "^4.1.0"
+  }
+}