### Summary
This PR fixes two issues that prevented the Agent component's
single-component debug/test run from working under the Go backend:
1. **Dynamic input_form generation**: Some components (e.g. `Agent`) do
not store a static `input_form` in the DSL. The Go handler now falls
back to the runtime component's `GetInputForm()` method, matching
Python's `Canvas.get_component_input_form` behavior. This resolves the
frontend 102 error: `component has no input_form`.
2. **Tenant ID injection for debug**: Single-component debug runs use a
fresh `CanvasState` that previously lacked `tenant_id`.
`AgentComponent.Invoke` resolves LLM credentials via the tenant tables,
so the debug run failed with `api key is required`. The handler now
seeds `state.Sys["tenant_id"]` with the authenticated user's ID,
mirroring Python's `@add_tenant_id_to_kwargs` decorator.
### Changes
- `internal/handler/agent_component.go`:
- Added `componentInputForm` helper that first reads the static
`input_form` and, if missing, instantiates the component and calls
`GetInputForm()`.
- In `DebugComponent`, set `debugState.Sys["tenant_id"] = user.ID`
before invoking the component.
