[EPIC]: General Typing And Validation #1995

Description

• Validate all backend requests and responses (either auto generate zod schemas from openapi or direct openapi client generation or custom zod schemas)
• Type everything as strict as possible -> no strings which could be const object enums or enums, null instead of 0 for relations which are not set, no any or unknown wherever possible
• Typed components (ht table, select)