IAV-1166: simplify AddAccountModal to use DynamicCredentialForm for all integrations
- Remove all external config view imports (Teams, Slack, Shopify, WordPress, Wix, Facebook, Instagram, SAV views) and use DynamicCredentialForm exclusively
- Add styled integration guide steps (wizard-inspired: gradient numbers, hover animations, shine overlay, docs link) in configuration step
- Show guide steps for all agents of the same integration (no longer conditional on config view type)
- Remove duplicate guide sections from 7 dedicated config view files
- Return null instead of "Aucune configuration requise" in DynamicCredentialForm when no schema is available
- Restore scrollbar styles on modal container