feat(studio): add visual agent creation workflow

[evanlowe]

Summary

• Add a visual Agent creation canvas with shared navigation, a blank-canvas Agent placeholder, and workflow editing.
• Connect generated Agent chat output to the authoritative nested draft used by the canvas, configuration panel, and deployment view.
• Present sequential workflows directly without exposing the internal wrapper concept.
• Render direct sub-Agents by default in an alternating side layout, with automatic fit and dedicated center handles for solid sequential edges.
• Add Agent configuration, comparison debugging, and deployment workspaces that reuse the same Agent names and data.
• Update the bundled Studio frontend and regression coverage.

Validation

• npm test — 805 passed
• npm run build — passed
• .venv/bin/pytest tests/cli/test_generated_agent_component_matrix.py tests/cli/test_generated_agent_planner.py — 84 passed, 7 skipped
• .venv/bin/pre-commit run --all-files — passed
• Visual review — 1440×900 and 390×844