refactor: consolidate config types and remove file-based config

Tickets: #2, #3

- Remove duplicate type definitions from shared/lib/config.ts
- Import types from schema files (game-settings.ts, guild-settings.ts)
- Add GuildConfig interface to guild-settings.ts schema
- Rename ModerationConfig to ModerationCaseConfig in moderation.service.ts
- Delete shared/config/config.json and shared/scripts/migrate-config-to-db.ts
- Update settings API to use gameSettingsService exclusively
- Return DB format (strings) from API instead of runtime BigInts
- Fix moderation service tests to pass config as parameter

Breaking Changes:
- Removes legacy file-based configuration system
- API now returns database format with string values for BigInt fields

shared/db/schema/guild-settings.ts

@@ -10,6 +10,26 @@ import { relations, type InferSelectModel, type InferInsertModel } from 'drizzle
 export type GuildSettings = InferSelectModel<typeof guildSettings>;
 export type GuildSettingsInsert = InferInsertModel<typeof guildSettings>;
 
+export interface GuildConfig {
+    studentRole?: string;
+    visitorRole?: string;
+    colorRoles: string[];
+    welcomeChannelId?: string;
+    welcomeMessage?: string;
+    feedbackChannelId?: string;
+    terminal?: {
+        channelId: string;
+        messageId: string;
+    };
+    moderation: {
+        cases: {
+            dmOnWarn: boolean;
+            logChannelId?: string;
+            autoTimeoutThreshold?: number;
+        };
+    };
+}
+
 export const guildSettings = pgTable('guild_settings', {
     guildId: bigint('guild_id', { mode: 'bigint' }).primaryKey(),
     studentRoleId: bigint('student_role_id', { mode: 'bigint' }),