feat: caller context cache invalidation endpoint

- CallerContextService: added invalidateCache(leadId) method
- CallerResolutionController: POST /api/caller/invalidate-context
  endpoint — frontend calls after appointment mutations to bust
  stale AI context cache

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/caller/caller-resolution.controller.ts

@@ -33,4 +33,13 @@ export class CallerResolutionController {
 
         return result;
     }
+
+    @Post('invalidate-context')
+    async invalidateContext(@Body('leadId') leadId: string) {
+        if (!leadId) {
+            throw new HttpException('leadId is required', HttpStatus.BAD_REQUEST);
+        }
+        await this.callerContext.invalidateCache(leadId);
+        return { status: 'ok' };
+    }
 }