fix(config): cover requirements-based FastAPI builds

Preserve contributor history and current-main behavior while resolving the exact reviewed follow-up.

Source-PR: https://github.com/affaan-m/ECC/pull/2988
Source-Parent: 2f0df4ed80
Review-Manifest-SHA256: b927e8ab52f3e7e60a30d9eb4954e5af52258df97b60807319c0c1cdb64bb742

config/project-stack-mappings.json

@@ -503,7 +503,7 @@
         "verification-loop"
       ],
       "commands": {
-        "build": ["pip install -e ."],
+        "build": ["pip install -r requirements.txt", "pip install -e ."],
         "test": ["pytest", "python -m pytest"],
         "lint": ["ruff check .", "mypy ."],
         "format": ["ruff format .", "black ."]