Publish Vulpes Preview 15 sources for desktop, Android and Tundra

Share Gaia assets and adapters, keep private profiles and development documents local, and update both public READMEs.

.gitignore

@@ -0,0 +1,21 @@
+/engines/
+/downloads/
+/profiles/
+/logs/
+__pycache__/
+*.pyc
+# Installed app payload is versioned; these indexes are generated by the server.
+/assets/registry.json
+/assets/build-info.json
+/assets/settings-current-defaults.json
+/node_modules/
+/npm-debug.log*
+/.venv/
+*.keystore
+*.jks
+.env
+.env.*
+/local.properties
+
+# Old B2G registry is unused by the modern host and contains historical paths.
+/assets/webapps/webapps.json