⚙️ Prepare v3 release: module path, version window, 3.0.0

Bump the Hugo module path to /v3, adopt a rolling latest-4 Hugo
version window (bot keeps it sliding), document new opt-in params,
and set package version to 3.0.0.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "hugo-blowfish-theme",
-  "version": "2.106.0",
+  "version": "3.0.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "hugo-blowfish-theme",
-      "version": "2.106.0",
+      "version": "3.0.0",
       "hasInstallScript": true,
       "license": "MIT",
       "dependencies": {