fix(ci): pin pytest==8.3.4 + pytest-asyncio==0.24.0 exact versions

Both requirements.txt and requirements-dev.txt had conflicting
minimum-version specs for pytest-asyncio (>=0.23 vs >=0.24).
pip resolved to latest available which may have breaking changes
(pytest-asyncio 0.25+ changed asyncio_mode behavior).

Pin to exact known-good versions:
- pytest==8.3.4 (last stable 8.3.x)
- pytest-asyncio==0.24.0 (matches asyncio_default_fixture_loop_scope)
- aiosqlite==0.20.0 (pinned for SQLite CI compatibility)

https://claude.ai/code/session_01W1rJthWDkasijTdXCfxVHs

salesflow-saas/backend/requirements-dev.txt

@@ -1,5 +1,5 @@
 # Dev / CI — not required in production images
-pytest>=8.0.0,<8.4.0
+pytest==8.3.4
-pytest-asyncio>=0.24.0,<0.26.0
+pytest-asyncio==0.24.0
-aiosqlite>=0.20.0,<0.21.0
+aiosqlite==0.20.0
 httpx>=0.28.1,<0.29.0

salesflow-saas/backend/requirements.txt

@@ -62,8 +62,8 @@ prometheus-fastapi-instrumentator>=7.0.0  # Prometheus metrics
 structlog>=24.0.0            # Structured JSON logging with tenant context
 
 # === Testing ===
-pytest>=8.0.0
+pytest==8.3.4
-pytest-asyncio>=0.23.0       # Async test support
+pytest-asyncio==0.24.0         # Async test support — pinned for CI stability
 pytest-cov>=5.0.0            # Coverage reporting
 factory-boy>=3.3.0           # Test data factories for SQLAlchemy models