Add backend/frontend scaffolding with Oracle ADB wallet config

- Backend: Spring Boot 3 + WebFlux, JWT auth, Oracle ADB wallet,
  8 controllers/services/repositories (Auth~Tag), DTOs, exception handling
- Frontend: Next.js 15, TypeScript, Tailwind CSS, AuthContext,
  7 pages (dashboard, knowledge, chat, study, todos, habits, login)
- DB: V1 migration with 12 tables including VECTOR(1024) + HNSW index
- Ops: PM2 ecosystem config, deploy.sh, start-backend.sh
- CLAUDE.md: DB credentials replaced with env var references

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

.env.sample

@@ -5,17 +5,25 @@
 # ============================================
 
 # ---------------------
-# Database (Oracle 23ai)
+# Database (Oracle ADB)
 # ---------------------
-DB_HOST=localhost
-DB_SERVICE=FREEPDB1
-DB_USER=sundol
-DB_PASSWORD=
+ORACLE_WALLET_PATH=/path/to/wallet
+ORACLE_TNS_NAME=dbdf0q9672liizzd_medium
+ORACLE_USERNAME=admin
+ORACLE_PASSWORD=
 
 # ---------------------
 # JWT
 # ---------------------
 JWT_SECRET=
+JWT_ACCESS_TOKEN_EXPIRY=900000
+JWT_REFRESH_TOKEN_EXPIRY=604800000
+
+# ---------------------
+# Server
+# ---------------------
+SERVER_PORT=8080
+CORS_ORIGIN=http://localhost:3000
 
 # ---------------------
 # Google OAuth
@@ -27,7 +35,7 @@ GOOGLE_CLIENT_SECRET=
 # OCI GenAI
 # ---------------------
 OCI_COMPARTMENT_ID=
-OCI_REGION=us-chicago-1
+OCI_REGION=ap-seoul-1
 
 # ---------------------
 # YouTube (optional)
@@ -47,9 +55,3 @@ 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=