feat: add Kosli Learning Labs section

[dangrondahl]

Summary

• Adds a new Labs tab with 6 pages: landing page + 5 progressive labs (account setup → Flows/Trails → build controls → release controls → runtime controls)
• Renames and converts tutorials/get_familiar_with_Kosli.md → tutorials/try_kosli_locally.mdx with <Steps> components, updated title/description, and removal of the now-redundant Playground callout
• Moves lab images to images/labs/ following existing repo convention
• Updates docs.json: Labs tab (no icon), footer link updated from GitHub URL to /labs, redirect from old tutorial URL, navigation updated
• Adds cross-reference callouts in index.mdx, getting_started/install.md, and understand_kosli/what_is_kosli.md
• CLI installation and API key setup moved from Lab 2 into Lab 1, so Lab 2 opens directly with Kosli concepts

Test plan

• mint broken-links passes
• Labs tab appears in nav and all 5 lab pages render
• Images load from /images/labs/
• Footer "Labs" link routes to /labs
• Redirect from /tutorials/get_familiar_with_kosli → /tutorials/try_kosli_locally works
• Cross-reference callouts render correctly on install, what_is_kosli, and labs index pages