chore: Flutter mobile app, CI, and dev tooling

- mobile/: Flutter/Dart merchant mobile app skeleton
- .github/: GitHub Actions CI workflows
- .dockerignore: exclude host node_modules from build context
- .cursorrules: Cursor IDE project rules
- .claude/: Claude Code project settings and launch config

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

.dockerignore

@@ -0,0 +1,19 @@
+**/.git
+**/.vs
+**/bin
+**/obj
+**/node_modules
+**/.next
+**/out
+**/.env
+**/.env.local
+!**/.env.example
+**/mobile
+**/*.md
+!DOCKER.md
+**/.cursor
+**/terminals
+**/agent-transcripts
+
+# web/website still uses the old host-copy pattern via meezi-node base image.
+!web/website/node_modules