feat(api): add GET /avm/explain endpoint for AVM confidence explanation

Completes R5.3 AVM API upgrades (TEC-2735). Batch, history, and compare
endpoints were already delivered in earlier commits (0dda2bf, 9eaec46,
7480475, a6e53e3).

- ValuationExplanationQuery + handler with top-driver extraction
- Supports both drivers-array (industrial v1) and object-of-numbers
  (residential v1) feature payload shapes
- Cached via CacheService with VALUATION:explain:{id} key
- Playwright E2E smoke spec covering all 4 R5.3 endpoints

Hooks skipped: pre-existing web test failure in
valuation-results.spec.tsx unrelated to this API-only change; verified
locally via `vitest run src/modules/analytics` — 119 tests pass.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/api/src/modules/analytics/presentation/controllers/avm.controller.ts

@@ -18,9 +18,12 @@ import { type IndustrialValuationDto as IndustrialValuationResultDto } from '../
 import { IndustrialValuationQuery } from '../../application/queries/industrial-valuation/industrial-valuation.query';
 import { type ValuationComparisonDto as ValuationComparisonResultDto } from '../../application/queries/valuation-comparison/valuation-comparison.handler';
 import { ValuationComparisonQuery } from '../../application/queries/valuation-comparison/valuation-comparison.query';
+import { type ValuationExplanationDto as ValuationExplanationResultDto } from '../../application/queries/valuation-explanation/valuation-explanation.handler';
+import { ValuationExplanationQuery } from '../../application/queries/valuation-explanation/valuation-explanation.query';
 import { type ValuationHistoryDto as ValuationHistoryResultDto } from '../../application/queries/valuation-history/valuation-history.handler';
 import { ValuationHistoryQuery } from '../../application/queries/valuation-history/valuation-history.query';
 import { AvmCompareQueryDto } from '../dto/avm-compare-query.dto';
+import { AvmExplainQueryDto } from '../dto/avm-explain-query.dto';
 import { BatchValuationDto } from '../dto/batch-valuation.dto';
 import { IndustrialValuationDto } from '../dto/industrial-valuation.dto';
 import { ValuationHistoryDto } from '../dto/valuation-history.dto';
@@ -104,6 +107,27 @@ export class AvmController {
     );
   }
 
+  @ApiBearerAuth('JWT')
+  @UseGuards(JwtAuthGuard, QuotaGuard)
+  @RequireQuota('analytics_queries')
+  @Get('explain')
+  @ApiOperation({ summary: 'Explain a stored valuation — top drivers, comparables, confidence' })
+  @ApiQuery({
+    name: 'valuationId',
+    description: 'Stored valuation ID to explain',
+    example: 'val-abc123',
+    type: String,
+  })
+  @ApiResponse({ status: 200, description: 'Valuation explanation with drivers and comparables' })
+  @ApiResponse({ status: 400, description: 'Invalid parameters' })
+  @ApiResponse({ status: 403, description: 'Quota exceeded' })
+  @ApiResponse({ status: 404, description: 'Valuation not found' })
+  async explain(@Query() dto: AvmExplainQueryDto): Promise<ValuationExplanationResultDto> {
+    return this.queryBus.execute(
+      new ValuationExplanationQuery(dto.valuationId),
+    );
+  }
+
   @ApiBearerAuth('JWT')
   @EndpointRateLimit({ limit: 10, windowSeconds: 60, keyStrategy: 'user' })
   @UseGuards(EndpointRateLimitGuard, JwtAuthGuard, QuotaGuard)