Fix Broken Form Submission

PROJECT CONTEXT:
Forms in my app fail silently, lose data, never reach the backend, or show success without saving anything.

GOAL:
Every form validates properly, submits to a real endpoint, persists data, and handles failure without losing input.

REQUIREMENTS:
- Inventory of every form and its intended effect
- Working submission to real endpoints
- Client and server validation with inline errors
- Loading states and double-submit protection
- Failure handling that preserves user input

CONSTRAINTS:
- A success toast without persisted data is a bug
- Validation must exist on the server too

DEFINITION OF DONE:
- Every form's submission persists and survives refresh
- Invalid input is caught inline before submission
- Failures show visible errors with input intact
- No form double-submits

COMMON FAILURES TO AVOID:
- Submit handlers that never call the API
- Forms clearing on failure and losing user input
- Validation only on the client, bypassable via direct calls
- Success messages regardless of outcome