Initial commit: project scaffold with android and backend submodules

Set up monorepo structure with git submodules:
- android/ -> SnapLedger-Android (Kotlin + Jetpack Compose)
- backend/ -> SnapLedger-Backend (Python FastAPI)

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

.gitignore

@@ -0,0 +1,15 @@
+# IDE
+.idea/
+.vscode/
+*.iml
+
+# OS
+.DS_Store
+Thumbs.db
+
+# Env
+.env
+.env.*
+
+# Claude
+.claude/