feat: add configurable mode groups to award detail view

Add per-award configurable mode groups for filtering multiple modes
together in the award detail view. Mode groups are displayed with
visual separators in the mode filter dropdown.

Backend changes:
- Add modeGroups to getAllAwards() return mapping
- Add getAwardById() function to fetch single award definition
- Add GET /api/awards/:awardId endpoint

Frontend changes:
- Fetch award definition separately to get modeGroups
- Update availableModes to include mode groups with separator
- Update filteredEntities logic to handle mode groups
- Update groupDataForTable() and applyFilter() for mode groups
- Disable separator option in dropdown

Award definitions:
- DXCC: Add Digi-Modes, Classic Digi-Modes, Mixed-Mode w/o WSJT-Modes,
  Phone-Modes groups
- DLD: Add same mode groups (adjusted for available modes)

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

award-definitions/dld.json

@@ -4,6 +4,12 @@
   "description": "Deutschland Diplom - Confirm 100 unique DOKs on different bands/modes",
   "caption": "Contact and confirm stations with 100 unique DOKs (DARC Ortsverband Kennung) on different band/mode combinations. Each unique DOK on a unique band/mode counts as one point. Only DCL-confirmed QSOs with valid DOK information count toward this award.",
   "category": "darc",
+  "modeGroups": {
+    "Digi-Modes": ["FT8", "FT4", "MFSK", "PSK31", "RTTY"],
+    "Classic Digi-Modes": ["PSK31", "RTTY"],
+    "Mixed-Mode w/o WSJT-Modes": ["PSK31", "RTTY", "AM", "SSB", "FM", "CW"],
+    "Phone-Modes": ["AM", "SSB", "FM"]
+  },
   "rules": {
     "type": "dok",
     "target": 100,