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/src/domains/agents/router.py

@@ -0,0 +1,84 @@
+"""
+REST API routes for agents.
+"""
+from fastapi import APIRouter, HTTPException
+
+from src.domains.agents.base import get_agent, list_agents
+
+# Import agents to ensure they're registered
+import src.domains.agents.explore  # noqa: F401
+from src.domains.agents.schemas import (
+    AgentRunRequest,
+    AgentRunResponse,
+    AgentInfo,
+    AgentListResponse,
+)
+from src.shared.logging import logged, get_logger
+
+logger = get_logger(__name__)
+
+router = APIRouter(prefix="/agents", tags=["Agents"])
+
+
+@router.get("/", response_model=AgentListResponse)
+async def list_available_agents() -> AgentListResponse:
+    """List all available agents."""
+    agents = list_agents()
+    return AgentListResponse(
+        agents=[AgentInfo(**a) for a in agents]
+    )
+
+
+@router.post("/run", response_model=AgentRunResponse)
+@logged()
+async def run_agent(request: AgentRunRequest) -> AgentRunResponse:
+    """
+    Run an agent with the given prompt.
+
+    The agent will use tools to explore the codebase and answer questions.
+    """
+    # Get the requested agent
+    agent = get_agent(request.agent_type)
+    if not agent:
+        raise HTTPException(
+            status_code=400,
+            detail=f"Unknown agent type: {request.agent_type}"
+        )
+
+    try:
+        # Run the agent
+        response = await agent.run(
+            request.prompt,
+            working_dir=request.working_dir,
+        )
+
+        return AgentRunResponse(
+            response=response,
+            agent_type=request.agent_type,
+            success=True,
+        )
+
+    except Exception as e:
+        logger.exception(f"Agent execution failed: {e}")
+        return AgentRunResponse(
+            response="",
+            agent_type=request.agent_type,
+            success=False,
+            error=str(e),
+        )
+
+
+@router.get("/{agent_type}", response_model=AgentInfo)
+async def get_agent_info(agent_type: str) -> AgentInfo:
+    """Get information about a specific agent."""
+    agent = get_agent(agent_type)
+    if not agent:
+        raise HTTPException(
+            status_code=404,
+            detail=f"Agent not found: {agent_type}"
+        )
+
+    return AgentInfo(
+        name=agent.name,
+        description=agent.description,
+    )