feat(config): add RealClientMode infrastructure for multi-version support

Add client version mode support to enable version-specific behavior:

- Add Mode type with constants for all game versions (S1.0 through ZZ)
- Add ClientMode (string) and RealClientMode (Mode) to Config
- Add ClanMemberLimits to GameplayOptions for configurable clan sizes
- Add MaximumFP to GameplayOptions for festa points cap
- Parse ClientMode string to RealClientMode enum in LoadConfig
- Set sensible defaults (ZZ for mode, standard limits for clans)
- Update config.example.json with new fields

This enables cherry-picking version-specific fixes from main branch.

config.example.json

@@ -12,6 +12,7 @@
   "ScreenshotAPIURL": "",
   "DeleteOnSaveCorruption": false,
   "DevMode": true,
+  "ClientMode": "ZZ",
   "DevModeOptions": {
     "AutoCreateAccount": true,
     "CleanDB": false,
@@ -39,6 +40,7 @@
     "DisableBoostTime": false,
     "BoostTimeDuration": 120,
     "ClanMealDuration": 3600,
+    "ClanMemberLimits": [[0, 30], [3, 40], [7, 50], [10, 60]],
     "BonusQuestAllowance": 3,
     "DailyQuestAllowance": 1
   },