feat(architecture): Add ResponseInterceptor for consistent API response envelope (#839)

[Gezziy]

closes #374

Summary of Changes

• New Interceptor: Created ResponseInterceptor in src/common/interceptors/response.interceptor.ts to wrap all REST API success responses inside a standard { data, meta } envelope.
• Envelope Handling:
  • Standardizes raw arrays, objects, and primitives into { data: response, meta: {} }.
  • Auto-normalizes legacy pagination objects like { items: T[], total: number } or { data: T[], total: number } to { data: items, meta: { total } }.
  • Preserves already enveloped { data, meta } payloads without double-wrapping.
• Context & Safety Bypasses:
  • Automatically bypasses non-HTTP contexts (e.g., GraphQL queries/mutations and WebSocket connections).
  • Safely bypasses raw file downloads (detects response.headersSent, 204 No Content, 304 Not Modified, Buffer payloads, and StreamableFile instances).
• Global Registration: Registered ResponseInterceptor globally in main.ts.
• Unit Testing: Added 16 comprehensive unit tests in src/common/interceptors/response.interceptor.spec.ts validating all formatting rules and bypass cases.

Reason for Changes

Currently, REST API endpoints return inconsistent shapes (some raw arrays, some pagination objects, some enveloped objects). This forces the frontend to write custom parsing logic for each endpoint. Standardizing on a { data, meta } envelope allows the client to process responses consistently.

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