chore(ci): allowlist strands-crm next.config.ts

The check-config-files job blocked the strands-crm showcase PR
(examples/showcases/strands-crm/frontend/next.config.ts was not in
the build-config allowlist). Adding it next to strands-file-analyzer.

Author: jerelvelarde

.github/config-allowlist.txt

@@ -58,6 +58,7 @@ examples/showcases/research-canvas/frontend/next.config.ts
 examples/showcases/research-canvas/start/frontend/next.config.ts
 examples/showcases/scene-creator/next.config.ts
 examples/showcases/spreadsheet/next.config.mjs
+examples/showcases/strands-crm/frontend/next.config.ts
 examples/showcases/strands-file-analyzer/next.config.ts
 examples/showcases/todo/next.config.mjs
 examples/v1/_legacy/copilot-anthropic-pinecone/next.config.mjs