fix: harden web runtime and follow-up auth/db security fixes (#21)

## Summary
- harden the web runtime with JSON body limits, stricter generation input validation, rate limiting, and trusted Origin/Referer checks for cookie-authenticated mutations
- redact password-reset tokens from debug email transport logs and fail closed for unsupported email providers
- scope generation idempotency keys per user with a Prisma migration and regression coverage

## Testing
- docker build -f infra/docker/web.Dockerfile -t nroxy-web-check .
- docker run --rm --entrypoint sh nroxy-web-check -lc "pnpm --filter @nproxy/providers test && pnpm --filter @nproxy/db test && pnpm --filter @nproxy/web test"

Closes #14
Closes #7
Closes #8

Co-authored-by: sirily <sirily@git.shararam.party>
Reviewed-on: #21

docs/ops/deployment.md

@@ -23,6 +23,8 @@ Deploy on one VPS with Docker Compose.
 - Keep secrets in server-side environment files or a secret manager.
 - Back up PostgreSQL and object storage separately.
 - Prefer Telegram long polling to avoid an extra public webhook surface for the bot.
+- In non-production environments, set `EMAIL_PROVIDER=example` only when you explicitly want the built-in debug transport. It logs redacted email previews and must never emit live password-reset tokens.
+- Do not rely on implicit email fallbacks. Unsupported providers now fail fast at startup so misconfigured deployments do not silently drop password-reset or billing mail.
 
 ## Upgrade strategy
 - Build new images.