chore: update readme

[maxy-shpfy]

TL;DR

Restructured the README to lead with a getting started guide and added UI/architecture screenshots.

What changed?

• Moved the Getting started section (prerequisites, install/run instructions, seeding) to the top of the README, directly after the project introduction, so new users see it immediately
• Renamed the former "Getting started" section to Operation manual to better reflect its content
• Added a Terminology heading to the existing glossary items
• Removed inline PI_PROXY_URL/PI_PROXY_API_KEY values from the example pnpm dev command, directing users to .env instead
• Embedded two screenshots: shell-ui-1.png after the intro paragraph and slide-architecture-1.png after the project structure tree
• Added three new image assets under docs/assets/: shell-ui-1.png, slide-architecture-1.png, and shell-collage-1.png

How to test?

Review the rendered README on the repository's main page and confirm:

• The getting started steps appear near the top
• Both images render correctly at 500px width
• The operation manual/configuration content remains intact below the architecture section

Why make this change?

The previous README buried the getting started instructions after a long architectural overview, making onboarding harder than necessary. Promoting setup steps to the top and adding visual context (UI screenshot and architecture diagram) gives new contributors and users a faster path to running the project.

[maxy-shpfy]

• chore: update readme #57 👈 (View in Graphite)
• main

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