fix: revert giphy 10.x (styled-components API break), clean WelcomePage

@giphy/react-components@10.x calls styled-components internals
(mergeAttributes) that do not exist in styled-components v6 — crashes
on open. Reverted to 1.6.0 until giphy publishes a v6-compatible release.

WelcomePage: remove Sentry test button (verified working), rename
Support -> Lotus Matrix Guide.

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

package.json

@@ -68,8 +68,8 @@
     "@atlaskit/pragmatic-drag-and-drop-hitbox": "1.1.0",
     "@fontsource/inter": "4.5.14",
     "@giphy/js-fetch-api": "5.8.0",
-    "@giphy/js-types": "5.1.0",
-    "@giphy/react-components": "10.1.2",
+    "@giphy/js-types": "4.3.0",
+    "@giphy/react-components": "1.6.0",
     "@sentry/react": "10.53.1",
     "@tanstack/react-query": "5.100.11",
     "@tanstack/react-query-devtools": "5.100.11",