[Refactor] Zod validation errors are returned as semicolon-joined strings — not machine-parseable

[RUKAYAT-CODER]

Overview

src/lib/validation.ts formats Zod errors by joining all issue messages with '; ' into a single string. Client-side code cannot programmatically distinguish which field failed or display field-specific inline errors. Every frontend form must parse a freeform string to show proper per-field validation feedback.

Specifications

Features:

• Validation error responses include a structured array of { field, message } objects
• Clients can map errors to specific form fields without string parsing

Tasks:

• Change validateBody() error response to: { errors: zodResult.error.issues.map(i => ({ field: i.path.join('.'), message: i.message })) }
• Update the HTTP error response body to { message: 'Validation failed', errors: [...] }
• Update all frontend form error handlers to consume the structured format
• Update API tests that assert on the error string format

Impacted Files:

• src/lib/validation.ts
• All API route files using validateBody()
• Frontend form components handling API validation errors

Acceptance Criteria

• Error responses include a structured errors array with field and message per issue
• Frontend forms display per-field error messages from the API response
• No semicolon-joined error string format remains