feat(security): address findings from v2 security assessment

- L2: Add server_tokens off to nginx configs to hide version
- M1: Add X-Frame-Options, X-Content-Type-Options, Referrer-Policy,
  Permissions-Policy headers to all nginx routes
- L3: Add global NoCacheInterceptor (Cache-Control: no-store) on all
  API responses to prevent caching of sensitive financial data
- C1: Disable open registration by default (ALLOW_OPEN_REGISTRATION env)
- H3: Add logout endpoint with correct HTTP 200 status code
- M2: Implement full password reset flow (forgot-password, reset-password,
  change-password) with hashed tokens, 15-min expiry, single-use
- Reduce JWT access token expiry from 24h to 1h
- Add EmailService stub (logs to shared.email_log)
- Add DB migration 016 for password_reset_tokens table

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

backend/src/app.module.ts

@@ -1,5 +1,5 @@
 import { Module, MiddlewareConsumer, NestModule } from '@nestjs/common';
-import { APP_GUARD } from '@nestjs/core';
+import { APP_GUARD, APP_INTERCEPTOR } from '@nestjs/core';
 import { ConfigModule, ConfigService } from '@nestjs/config';
 import { TypeOrmModule } from '@nestjs/typeorm';
 import { ThrottlerModule } from '@nestjs/throttler';
@@ -7,6 +7,7 @@ import { AppController } from './app.controller';
 import { DatabaseModule } from './database/database.module';
 import { TenantMiddleware } from './database/tenant.middleware';
 import { WriteAccessGuard } from './common/guards/write-access.guard';
+import { NoCacheInterceptor } from './common/interceptors/no-cache.interceptor';
 import { AuthModule } from './modules/auth/auth.module';
 import { OrganizationsModule } from './modules/organizations/organizations.module';
 import { UsersModule } from './modules/users/users.module';
@@ -95,6 +96,10 @@ import { ScheduleModule } from '@nestjs/schedule';
       provide: APP_GUARD,
       useClass: WriteAccessGuard,
     },
+    {
+      provide: APP_INTERCEPTOR,
+      useClass: NoCacheInterceptor,
+    },
   ],
 })
 export class AppModule implements NestModule {