fix(ci): run lint commands directly with uv run instead of bash script

The issue was that 'uv run bash scripts/lint.sh' doesn't activate the venv
for the bash subprocess, so commands inside the script can't find tools.

Solution: Run lint commands directly in workflow with 'uv run' prefix:
- uv run mypy app
- uv run ruff check app
- uv run ruff format app --check

This is the recommended approach per uv documentation and GitHub issue fastapi#1910.
The bash script approach doesn't work because bash subprocess doesn't inherit
the activated environment.

Related to CUR-29

🤖 Generated by Aygentic

Co-Authored-By: Aygentic <noreply@aygentic.com>

Author: amostt

.github/workflows/lint-backend.yml

@@ -27,8 +27,8 @@ jobs:
       - name: Install dependencies
         run: uv sync
         working-directory: backend
-      - name: Run linters
-        run: uv run bash scripts/lint.sh
+      - name: Run mypy
+        run: uv run mypy app
         working-directory: backend
         env:
           # Required env vars for Settings class initialization during mypy analysis
@@ -44,3 +44,9 @@ jobs:
           REDIS_URL: redis://:dummy@localhost:6379/0
           CELERY_BROKER_URL: redis://:dummy@localhost:6379/0
           CELERY_RESULT_BACKEND: redis://:dummy@localhost:6379/0
+      - name: Run ruff check
+        run: uv run ruff check app
+        working-directory: backend
+      - name: Run ruff format check
+        run: uv run ruff format app --check
+        working-directory: backend