Initial project setup with env template and gitignore

- .gitignore: Java/Maven, Node.js, IDE, OS, credentials
- .env.sample: backend + frontend environment variable template
- README.md: project overview and getting started guide
- CLAUDE.md: development rules and guidelines
- docs/: SUNDOL spec and design patterns guide

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.env.sample

@@ -0,0 +1,55 @@
+# ============================================
+# SUNDOL Environment Variables
+# Copy this file to .env and fill in values
+#   cp .env.sample .env
+# ============================================
+
+# ---------------------
+# Database (Oracle 23ai)
+# ---------------------
+DB_HOST=localhost
+DB_SERVICE=FREEPDB1
+DB_USER=sundol
+DB_PASSWORD=
+
+# ---------------------
+# JWT
+# ---------------------
+JWT_SECRET=
+
+# ---------------------
+# Google OAuth
+# ---------------------
+GOOGLE_CLIENT_ID=
+GOOGLE_CLIENT_SECRET=
+
+# ---------------------
+# OCI GenAI
+# ---------------------
+OCI_COMPARTMENT_ID=
+OCI_REGION=us-chicago-1
+
+# ---------------------
+# YouTube (optional)
+# ---------------------
+YOUTUBE_API_KEY=
+
+# ---------------------
+# Redis
+# ---------------------
+REDIS_HOST=localhost
+REDIS_PORT=6379
+
+# ---------------------
+# Frontend (Next.js)
+# ---------------------
+NEXT_PUBLIC_API_URL=http://localhost:8080
+NEXTAUTH_URL=http://localhost:3000
+NEXTAUTH_SECRET=
+API_URL=http://localhost:8080
+
+# ---------------------
+# Gitea
+# ---------------------
+GITEA_USER=joungmin
+GITEA_PASSWORD=