Use recursive globs in lint workflow

Update .github/workflows/lint-backend.yml to use recursive glob patterns for Python files so changes in nested subdirectories trigger the lint workflow. Replaced 'src/**.py' with 'src/**/*.py' and 'tests/**.py' with 'tests/**/*.py'.

Author: edwinjosechittilappilly

.github/workflows/lint-backend.yml

@@ -3,8 +3,8 @@ name: Lint Backend
 on:
   pull_request:
     paths:
-      - 'src/**.py'
-      - 'tests/**.py'
+      - 'src/**/*.py'
+      - 'tests/**/*.py'
       - 'pyproject.toml'
       - 'uv.lock'
       - '.github/workflows/lint-backend.yml'