Record and embed the hero terminal demo (asciinema/GIF) with a CI size guard

[ivklgn]

Problem

The README has no hero demo — there is no asciinema cast or GIF showing Archcore in action, and no .github/assets/readme-hero.* asset. Text alone under-sells the "describe intent → routed to the right document" experience.

Expected result

A short (<=20s) recorded demo — a user types "record the decision to use PostgreSQL", the agent auto-routes to /archcore:decide, and an ADR appears with a relation suggestion — hosted (asciinema SVG or a committed GIF), embedded at the top of the README with descriptive alt text. If a GIF is committed, a CI check fails when the asset exceeds 2 MB.

Impact

Shows the core loop in motion, which converts far better than prose, while the size guard keeps the repository lean.

Proposed approach

• Record and host the cast/GIF; embed with alt text.
• (If GIF) add a CI size check (<= 2 MB).

Acceptance criteria

• The demo is embedded at the top of the README with alt text.
• If committed as a GIF, CI fails when it exceeds 2 MB.

References

Design rationale: .archcore/plugin/readme-first-60-seconds.idea.md (status: draft). Separable from the README hero-section issue because it needs an external recording. Code: README.md, .github/.