refactor: reorganize into monorepo with separate subprojects

Structure webber into three independent subprojects:
- webber-api/: FastAPI backend server with all agent code
- webber-cli/: Standalone CLI client (renamed from cli/ to webber_cli/)
- webber-sandbox/: Test project for functional testing

Key changes:
- Each subproject has its own .venv (Python 3.12+)
- Added sandbox.sh for managing test project templates
- Created sandbox-templates/ with calculator-cli and empty starter
- Updated CI/CD for prefixed tags (api/v*, cli/v*)
- Added comprehensive AGENTS.md with operational instructions
- Added gitignore filtering to glob and grep tools
- Created pyproject.toml for each subproject

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

webber-api/tests/conftest.py

@@ -0,0 +1,34 @@
+"""
+Pytest configuration and fixtures.
+"""
+import pytest
+from httpx import ASGITransport, AsyncClient
+
+from src.main import app
+
+
+@pytest.fixture
+def anyio_backend():
+    """Use asyncio for async tests."""
+    return "asyncio"
+
+
+@pytest.fixture
+async def client():
+    """Async HTTP client for testing."""
+    async with AsyncClient(
+        transport=ASGITransport(app=app),
+        base_url="http://test"
+    ) as ac:
+        yield ac
+
+
+@pytest.fixture
+async def auth_client():
+    """Async HTTP client with API key for authenticated requests."""
+    async with AsyncClient(
+        transport=ASGITransport(app=app),
+        base_url="http://test",
+        headers={"X-API-Key": "test-api-key"}
+    ) as ac:
+        yield ac