BUG: Multiple database integrity issues in schema.sql missing therapy_type table, no unique constraint on assessment_results, and no ON DELETE rules on foreign keys

### Is there an existing issue for this?

- [x] I have searched the existing issues

### What happened?

## 📌 Issue Overview

`supabase/schemas/schema.sql` has three related database integrity problems that together make the schema non-executable from scratch, allow duplicate medical records, and leave orphaned rows on user deletion.
## 🔍 Steps to Reproduce
**Issue 1 — Missing therapy_type table:**
1. Run `schema.sql` against a fresh Postgres/Supabase instance.
2. Observe: `ERROR: relation "therapy_type" does not exist` on `therapy_goal` creation.

**Issue 2 — Duplicate assessment submissions:**
1. Open the assessment submission screen on a slow connection.
2. Tap submit twice before the response returns.
3. Two rows now exist in `assessment_results` for the same `patient_id` + `assessment_id`.

**Issue 3 — No ON DELETE behavior:**
1. Insert a patient with linked sessions, activity logs, and assessment results.
2. Attempt to delete the patient record.
3. Observe either a FK violation error or orphaned rows left in child tables.

## 🎯 Expected Behavior

- Schema should be executable from scratch without errors.
- Each patient should have at most one result per assessment.
- Deleting a patient should cascade to their owned data; deleting a therapist should set `therapist_id` to NULL in related records.
## 🚨 Actual Behavior

- `therapy_goal` references `therapy_type(id)` which does not exist in the schema.
- Duplicate assessment results can be silently inserted into medical records.
- No `ON DELETE` rules defined anywhere — orphaned data or blocked deletions.
## 📷 Screenshot

N/A
## 💡 Suggested Improvements

- Add `CREATE TABLE therapy_type` before `therapy_goal` in `schema.sql`.
- Add `CONSTRAINT uq_patient_assessment UNIQUE (patient_id, assessment_id)` to `assessment_results`.
- Add `ON DELETE CASCADE` or `ON DELETE SET NULL` to all foreign keys based on relationship semantics.
- Change `.insert()` to `.upsert()` with `onConflict: 'patient_id,assessment_id'` in the Edge Function.

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