Add bulk price editing features and fix quantity update price preservation

- Fix FilamentForm to preserve prices when updating quantities
  - Add isInitialLoad flag to prevent price override on form load
  - Only update prices when color is actively changed, not on initial render

- Add bulk filament price editor to dashboard
  - Filter by material and finish
  - Set refill and/or spool prices for multiple filaments
  - Preview changes before applying
  - Update all filtered filaments at once

- Add bulk color price editor to colors page
  - Edit prices for all colors in one interface
  - Global price application with search filtering
  - Individual price editing with change tracking

- Add auto-kill script for dev server
  - Kill existing processes on ports 3000/3001 before starting
  - Prevent "port already in use" errors
  - Clean start every time npm run dev is executed

package.json

@@ -3,7 +3,7 @@
   "version": "1.0.0",
   "private": true,
   "scripts": {
-    "dev": "next dev",
+    "dev": "./scripts/kill-dev.sh && next dev",
     "build": "next build",
     "start": "next start",
     "lint": "next lint",