Merge PR #48: feat: add Xiaohongshu source + Reddit public fallback

- Xiaohongshu search via local MCP service (opt-in, zero impact if service not running)
- Reddit public JSON fallback (works with zero API keys)
- Reddit priority: ScrapeCreators -> OpenAI -> public fallback
- Updated env.py: Reddit always available via public fallback

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

vendor/package/dist/lib/features.json

@@ -0,0 +1,17 @@
+{
+  "global": {
+    "responsive_web_grok_annotations_enabled": false,
+    "post_ctas_fetch_enabled": true,
+    "responsive_web_graphql_exclude_directive_enabled": true
+  },
+  "sets": {
+    "lists": {
+      "blue_business_profile_image_shape_enabled": true,
+      "tweetypie_unmention_optimization_enabled": true,
+      "responsive_web_text_conversations_enabled": false,
+      "interactive_text_enabled": true,
+      "vibe_api_enabled": true,
+      "responsive_web_twitter_blue_verified_badge_is_enabled": true
+    }
+  }
+}