refactor: migrate interfaces to dedicated directory

Reorganizes TypeScript interfaces into a modular structure:
- Create dedicated interfaces directory with specialized files
- Split interfaces by domain (claims, common, limits, records, user)
- Update imports in endorserServer.ts to use new interface locations
- Replace 'any' types with 'unknown' for better type safety
- Add proper type imports and exports

This improves code organization and maintainability by:
- Centralizing interface definitions
- Reducing file size of endorserServer.ts
- Making interface relationships more explicit
- Improving type safety with stricter types

src/interfaces/limits.ts

@@ -0,0 +1,14 @@
+export interface EndorserRateLimits {
+  doneClaimsThisWeek: string;
+  doneRegistrationsThisMonth: string;
+  maxClaimsPerWeek: string;
+  maxRegistrationsPerMonth: string;
+  nextMonthBeginDateTime: string;
+  nextWeekBeginDateTime: string;
+}
+
+export interface ImageRateLimits {
+  doneImagesThisWeek: string;
+  maxImagesPerWeek: string;
+  nextWeekBeginDateTime: string;
+}