[Good first issue]: Add Codespaces first-run timing notes

[morning-verlu]

Goal

Improve the browser-only onboarding path by documenting what a first-time Codespaces user should expect.

Suggested scope

• Update docs/CODESPACES.md or START_HERE.md.
• Add a short note about dev container startup taking a few minutes.
• Point users to ./scripts/codespaces-smoke.sh and build/install/kaios-cli/bin/kaios tour.
• Include the smallest useful troubleshooting note if the first command is run before the build finishes.

Verification

For a docs-only PR, run:

git diff --check

If you can use Codespaces, also paste whether ./scripts/codespaces-smoke.sh passed.

Notes

Keep this practical and short. The goal is to reduce first-run confusion, not add a full Codespaces tutorial.

[sarkarshrayan2-max]

Hi, I'd like to work on this issue if additional contributions are still needed.