Handbook + customer docs for the agent and App Market server lane

Imported from GitHub issue El-SaMa/oma#157 by @El-SaMa.

• Staff handbook page: architecture, enrolment, revoke, troubleshooting
• Customer tutorial course (HTML sections, step cards, real shots), fi + en native
• Product page in showcase style (Cloudways style, but ours)

Design doc: https://claude.ai/code/artifact/8e38762a-5369-45d1-a64d-fce59d2e560b