feat: add achievements system to awards with mode filter support

Implement achievements milestone feature for awards with configurable
levels (Silver, Gold, Platinum, etc.) that track progress beyond the
base award target. Achievements display earned badges and progress bar
toward next level.

Backend:
- Add calculateAchievementProgress() helper in awards.service.js
- Include achievements field in getAllAwards() and getAwardById()
- Add achievements validation in awards-admin.service.js
- Update PUT endpoint validation schema to include achievements field

Frontend:
- Add achievements section to award detail page with gold badges
- Add reactive achievement progress calculation that respects mode filter
- Add achievements tab to admin create/edit pages with full CRUD

Award Definitions:
- Add achievements to DXCC (100/200/300/500)
- Add achievements to DLD (50/100/200/300)
- Add achievements to WAS (30/40/50)

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

src/backend/index.js

@@ -1607,6 +1607,7 @@ const app = new Elysia()
         category: t.String(),
         rules: t.Any(),
         modeGroups: t.Optional(t.Any()),
+        achievements: t.Optional(t.Any()),
       }),
     }
   )