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.

.gitignore

@@ -29,6 +29,9 @@ Thumbs.db
 .env
 .claude/
 
+# Per-deploy build configuration (yarn configure)
+/.nitro-build.json
+
 # Local runtime config copies
 /public/configuration/renderer-config.json
 /public/configuration/ui-config.json