Simplify quickstart and UI quickstart onboarding

[soumya-io]

Summary

• Quickstart: docker compose is now the default path — the one-liner setup is Steps 1-2 instead of a Tip box. The clone-the-repo workflow is collapsed into an <Accordion> for contributors.
• Quickstart: single-file control setup — merged the split agent-registration + control-creation scripts into a streamlined two-file flow (setup_control.py creates the control, my_agent.py runs the agent). Removes the redundant double-registration and cuts the step count from 4 to 3.
• UI Quickstart: leads with "open localhost:8000" — since the docker compose setup already includes the UI, the page now opens with the dashboard URL. Manual Node/pnpm setup is collapsed into an <Accordion> for source-runners only.
• UI Quickstart: removed "Regenerate API Types" — this is a contributor concern, not part of the onboarding flow.

Net result: -184 lines, fewer prerequisites to parse, and a clear copy → paste → run path.

Test plan

• Verify quickstart.mdx renders correctly — Accordion expands/collapses, code blocks copy cleanly
• Verify ui-quickstart.mdx renders correctly — Accordion for manual setup works
• Walk through the 3-step flow end-to-end: docker compose → setup_control.py → my_agent.py
• Confirm the UI dashboard loads at localhost:8000 after docker compose

🤖 Generated with Claude Code

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❌ Markdown Lint Issues Found

Markdownlint found issues in the changed markdown files. Please review and fix them:

Files checked:

core/quickstart.mdx core/ui-quickstart.mdx

To fix locally:

1. Install markdownlint-cli2:

   npm install -g markdownlint-cli2

2. Run on specific files:

   markdownlint-cli2 path/to/your/file.md

3. Or run on all files:

   markdownlint-cli2 "**/*.{md,mdx}" --config .markdownlint.jsonc

See the markdownlint rules documentation for details on each rule.