Fix TypeScript: export interfaces for controller return type resolution

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/src/modules/investment-planning/investment-planning.service.ts

@@ -5,7 +5,7 @@ import { DataSource } from 'typeorm';
 
 // ── Interfaces ──
 
-interface AccountBalance {
+export interface AccountBalance {
   id: string;
   account_number: string;
   name: string;
@@ -15,7 +15,7 @@ interface AccountBalance {
   balance: string;
 }
 
-interface InvestmentAccount {
+export interface InvestmentAccount {
   id: string;
   name: string;
   institution: string;
@@ -28,7 +28,7 @@ interface InvestmentAccount {
   current_value: string;
 }
 
-interface CdRate {
+export interface CdRate {
   bank_name: string;
   apy: string;
   min_deposit: string | null;
@@ -37,7 +37,7 @@ interface CdRate {
   fetched_at: string;
 }
 
-interface Recommendation {
+export interface Recommendation {
   type: 'cd_ladder' | 'new_investment' | 'reallocation' | 'maturity_action' | 'liquidity_warning' | 'general';
   priority: 'high' | 'medium' | 'low';
   title: string;
@@ -51,7 +51,7 @@ interface Recommendation {
   rationale: string;
 }
 
-interface AIResponse {
+export interface AIResponse {
   recommendations: Recommendation[];
   overall_assessment: string;
   risk_notes: string[];