## Summary
Adds the missing input form metadata for the Go BGPT canvas component.
## Root Cause
The standalone BGPT component was registered in Go, but it did not
implement GetInputForm(). During component trial run, the backend asks
the component for its input_form. Since BGPT had none, the API returned:
component has no input_form: BGPT:<node_id>
Python BGPT already exposes the query input form, so the Go component
needed the same contract.
## Change
Added GetInputForm() to the Go BGPT component with a single query line
input.
Added test coverage to ensure BGPT exposes the input form.
## Validation
Backend:
bash build.sh --test -run TestBGPT ./internal/agent/component
<img width="1369" height="1184" alt="image"
src="https://github.com/user-attachments/assets/f99e4a81-2359-42e5-80bb-dcc4e6a63fea"
/>
<img width="1736" height="1152" alt="image"
src="https://github.com/user-attachments/assets/c11240a5-2c42-4d08-88e3-c6dfbf49eedb"
/>
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