feat: interactive JSON / JSON5 mode selector at build time

Lets the operator pick between strict JSON (legacy) and JSON5 for every
configuration file consumed by Nitro and the renderer.

- scripts/configure-json.mjs: interactive prompt (JSON5 recommended),
  with --if-missing and --non-interactive flags for CI use
- package.json: yarn configure / prestart / prebuild hooks
- vite.config.mjs: reads .nitro-build.json (or NITRO_JSON_MODE env) and
  injects the compile-time constant __NITRO_JSON_MODE__ via define
- src/bootstrap.ts: routes client-mode.json parsing through the
  selected mode
- .gitignore: ignore the per-deployment .nitro-build.json
- README: full usage and override section
- public/configuration assets regenerated by the updated prebuild flow

The renderer side (@nitrots/utils JsonParser) is updated in the
companion Nitro_Render_V3 commit on the dev branch.

package.json

@@ -4,9 +4,11 @@
     "homepage": ".",
     "private": true,
     "scripts": {
-        "prebuild": "node scripts/write-asset-loader.mjs",
-        "start": "vite --host",
-        "build": "vite build && node scripts/minify-dist.mjs",
+        "configure": "node scripts/configure-json.mjs",
+        "prestart": "node scripts/configure-json.mjs --if-missing",
+        "prebuild": "node scripts/configure-json.mjs --if-missing && node scripts/write-asset-loader.mjs",
+        "start": "vite --base=/nitro/ --host",
+        "build": "vite build --base=/nitro/ && node scripts/minify-dist.mjs",
         "build:prod": "npx browserslist@latest --update-db && yarn build",
         "eslint": "eslint ./src"
     },