feat: add standalone form page, close all audit gaps, pass v1.0 milestone

Add standalone form page template that bypasses the theme, with admin
setting and auto-creation on plugin activation. Fix reCAPTCHA v3 double
submission, remove jQuery dependency, extend localized JS strings, and
overhaul form CSS/JS. Update milestone audit to PASSED (9/9, 10/10, 5/5).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.claude/settings.local.json

@@ -0,0 +1,9 @@
+{
+  "permissions": {
+    "allow": [
+      "Skill(gsd:audit-milestone)",
+      "WebSearch",
+      "Bash(wp i18n make-pot:*)"
+    ]
+  }
+}