Feature: Add third price option for plain/blank products

- Added plainPrice field to Product model in Prisma schema
- Updated database to include new plainPrice column
- Added Plain price input field to product creation form (new/page.tsx)
- Added Plain price input field to product edit form ([id]/edit/page.tsx)
- Updated createProduct server action to handle plainPrice
- Updated updateProduct server action to handle plainPrice

Now supports three price tiers:
- basePrice: for ready-made items
- plainPrice: for plain/blank items (new)
- personalisedPrice: for made-to-order items

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

.claude/settings.local.json

@@ -128,7 +128,13 @@
       "Bash(git commit -m 'Chore: Migrate database from SQLite to PostgreSQL on VM *)",
       "Bash(git pull *)",
       "Bash(git rm *)",
-      "Bash(git commit -m 'Chore: Remove .env from version control for security *)"
+      "Bash(git commit -m 'Chore: Remove .env from version control for security *)",
+      "Bash(git fetch *)",
+      "Bash(git ls-remote *)",
+      "Bash(timeout 30 git push origin main --force)",
+      "Bash(GIT_TRACE=1 git push origin main --force)",
+      "Bash(pkill -f \"node.exe\")",
+      "PowerShell(Stop-Process -Name node -Force -ErrorAction SilentlyContinue)"
     ]
   }
 }