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_agents_api.py

@@ -0,0 +1,75 @@
+"""
+Tests for agent REST API endpoints.
+"""
+import pytest
+
+
+class TestAgentListEndpoint:
+    """Tests for GET /agents/ endpoint."""
+
+    @pytest.mark.anyio
+    async def test_list_agents(self, auth_client):
+        """Test listing available agents."""
+        response = await auth_client.get("/agents/")
+
+        assert response.status_code == 200
+        data = response.json()
+        assert "agents" in data
+        assert len(data["agents"]) >= 1
+
+        # Check explore agent is present
+        agent_names = [a["name"] for a in data["agents"]]
+        assert "explore" in agent_names
+
+
+class TestAgentInfoEndpoint:
+    """Tests for GET /agents/{agent_type} endpoint."""
+
+    @pytest.mark.anyio
+    async def test_get_explore_agent_info(self, auth_client):
+        """Test getting explore agent info."""
+        response = await auth_client.get("/agents/explore")
+
+        assert response.status_code == 200
+        data = response.json()
+        assert data["name"] == "explore"
+        assert "description" in data
+
+    @pytest.mark.anyio
+    async def test_get_unknown_agent(self, auth_client):
+        """Test getting info for unknown agent."""
+        response = await auth_client.get("/agents/nonexistent")
+
+        assert response.status_code == 404
+
+
+class TestAgentRunEndpoint:
+    """Tests for POST /agents/run endpoint."""
+
+    @pytest.mark.anyio
+    async def test_run_with_unknown_agent(self, auth_client):
+        """Test running unknown agent type."""
+        response = await auth_client.post(
+            "/agents/run",
+            json={
+                "prompt": "test",
+                "agent_type": "nonexistent",
+                "working_dir": "."
+            }
+        )
+
+        assert response.status_code == 400
+        assert "Unknown agent" in response.json()["detail"]
+
+    @pytest.mark.anyio
+    async def test_run_request_validation(self, auth_client):
+        """Test request validation."""
+        # Missing required field
+        response = await auth_client.post(
+            "/agents/run",
+            json={
+                "working_dir": "."
+            }
+        )
+
+        assert response.status_code == 422  # Validation error