docs: add design spec for cf7-spam-to-telegram plugin

Independent WP plugin that forwards CF7 spam submissions to a Telegram group,
applying a weighted heuristic (client/unclear/spam) to help operators
spot real inquiries mistakenly filtered as spam.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,6 @@
+/vendor/
+/node_modules/
+composer.lock
+.phpunit.result.cache
+.DS_Store
+*.log