add linter for checking license headers (and eslint --fix target to match, and fix missing license headers while we're here) (#62)

package.json

@@ -12,6 +12,7 @@
     "test": "npm run test --workspaces",
     "start": "scripts/start.sh",
     "debug": "scripts/debug.sh",
+    "fix": "eslint . --fix",
     "lint": "eslint . --ext .ts,.tsx",
     "typecheck": "tsc --noEmit --jsx react",
     "format": "prettier --write .",
@@ -22,6 +23,7 @@
     "eslint": "^9.24.0",
     "eslint-config-prettier": "^10.1.2",
     "eslint-plugin-import": "^2.31.0",
+    "eslint-plugin-license-header": "^0.8.0",
     "eslint-plugin-react": "^7.37.5",
     "eslint-plugin-react-hooks": "^5.2.0",
     "globals": "^16.0.0",