feat: Add 5Why_ prefix to all database tables

- Rename all tables with 5Why_ prefix for namespace isolation
- Update models: User.js, Analysis.js, AuditLog.js
- Update routes: llmConfig.js
- Update scripts: seed-test-users.js, add-deepseek-config.js, add-ollama-config.js
- Add migrate-table-prefix.js script for database migration
- Update db_schema.sql with new table names
- Update views: 5Why_user_analysis_stats, 5Why_recent_analyses

Tables renamed:
- users -> 5Why_users
- analyses -> 5Why_analyses
- analysis_perspectives -> 5Why_analysis_perspectives
- analysis_whys -> 5Why_analysis_whys
- llm_configs -> 5Why_llm_configs
- system_settings -> 5Why_system_settings
- audit_logs -> 5Why_audit_logs
- sessions -> 5Why_sessions

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

scripts/seed-test-users.js

@@ -60,7 +60,7 @@ async function seedTestUsers() {
     for (const user of testUsers) {
       // 檢查使用者是否已存在 (只用 email 精確匹配)
       const [existing] = await connection.execute(
-        'SELECT id FROM users WHERE email = ?',
+        'SELECT id FROM 5Why_users WHERE email = ?',
         [user.email]
       );
 
@@ -68,7 +68,7 @@ async function seedTestUsers() {
         // 更新現有使用者的密碼
         const passwordHash = await bcrypt.hash(user.password, 10);
         await connection.execute(
-          'UPDATE users SET password_hash = ?, role = ?, is_active = 1, employee_id = ? WHERE email = ?',
+          'UPDATE 5Why_users SET password_hash = ?, role = ?, is_active = 1, employee_id = ? WHERE email = ?',
           [passwordHash, user.role, user.employee_id, user.email]
         );
         console.log(`🔄 Updated: ${user.email} (${user.role})`);
@@ -76,7 +76,7 @@ async function seedTestUsers() {
         // 建立新使用者
         const passwordHash = await bcrypt.hash(user.password, 10);
         await connection.execute(
-          `INSERT INTO users (employee_id, username, email, password_hash, role, department, position, is_active)
+          `INSERT INTO 5Why_users (employee_id, username, email, password_hash, role, department, position, is_active)
            VALUES (?, ?, ?, ?, ?, ?, ?, 1)`,
           [user.employee_id, user.username, user.email, passwordHash, user.role, user.department, user.position]
         );