[FEATURE] Add Censys module for certificate search

[NovaCode37]

Add Censys.io integration for certificate and host discovery,
as an alternative/complement to crt.sh.

Scope:

• New module: modules/censys_lookup.py
• Search certificates by domain
• Discover hosts and open ports
• Integrate into domain/IP scan pipeline
• Display in ScanResults.tsx

API:

• Censys Search API v2: https://search.censys.io/api
• Free tier: 250 queries/month

Env variable: CENSYS_API_ID + CENSYS_API_SECRET