Implement grower notes CRUD endpoints

**Description**

Add backend API endpoints to support the internal staff notes feature for grower profiles
https://github.com/Greenstand/treetracker-admin-client/issues/669

**Endpoints needed**

| Method | Endpoint | Description |
|--------|----------------------------------------------------|---------------------------------|
| GET | /api/{org}/planter/{growerId}/notes | Fetch all notes for a grower |
| POST | /api/{org}/planter/{growerId}/notes | Create a new note |
| PATCH | /api/{org}/planter/{growerId}/notes/{noteId} | Edit an existing note |
| DELETE | /api/{org}/planter/{growerId}/notes/{noteId} | Delete a note |

**New table grower_note:**

| Column | Type | Notes |
|--------------|----------------------|--------------------------------|
| id | serial (primary key) | |
| planter_id | integer | FK → planter.id |
| content | text | |
| author_id | integer | FK → admin_user.id |
| author_name | varchar | Denormalized for display |
| created_at | timestamp | |
| updated_at | timestamp | |