Initialize guideCity monorepo scaffolding

Set up git repo with .gitignore and README describing the planned
backend (FastAPI + PostGIS) and Android (Kotlin/Compose) architecture.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,36 @@
+# Environment
+.env
+*.env
+!.env.example
+
+# Python
+__pycache__/
+*.py[cod]
+*.egg-info/
+.venv/
+venv/
+.pytest_cache/
+.mypy_cache/
+.ruff_cache/
+
+# Docker
+docker-compose.override.yml
+
+# Android / Gradle
+android/local.properties
+android/.gradle/
+android/**/build/
+android/.idea/
+android/*.iml
+android/.cxx/
+android/captures/
+android/.externalNativeBuild/
+*.keystore
+*.jks
+
+# IDE
+.vscode/
+.DS_Store
+
+# Logs
+*.log