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/test_health.py

@@ -0,0 +1,29 @@
+"""
+Health endpoint tests.
+"""
+import pytest
+
+
+@pytest.mark.anyio
+async def test_root(client):
+    """Test root endpoint returns service info."""
+    response = await client.get("/")
+    assert response.status_code == 200
+
+    data = response.json()
+    assert "Webber" in data["service"]
+    assert data["status"] == "healthy"
+    assert "version" in data
+    assert data["docs"] == "/docs"
+
+
+@pytest.mark.anyio
+async def test_health_check(client):
+    """Test health check endpoint."""
+    response = await client.get("/health")
+    assert response.status_code == 200
+
+    data = response.json()
+    assert data["status"] == "healthy"
+    assert "Webber" in data["service"]
+    assert "version" in data