docs: rewrite README — content-first, drop GIFs, link to website

[fede-kamel]

Summary

The previous README leaned on three large demo GIFs (`hero.gif`, `oracle_26ai/demo.gif`, `build-an-agent.gif`) and stale exact-count test badges (`2,987 unit / 330+ integration`). With the docs site at https://oracle-samples.github.io/locus/ now the authoritative content source for diagrams, screenshots, and longer-form content, this README's job is the 30-second orientation that points readers there.

Changes

• Drop all 3 demo GIFs (the "weird videos").
• Keep the two informative SVG diagrams (`agent-loop.svg`, `architecture.svg`).
• Trim badges to status-style only — Python version, License, mypy strict, ruff clean, OCI day-0. No more brittle test counts.
• Tighter narrative flow (replaces the previous Architecture / One run end-to-end / Quick start / Capabilities sequence):
  1. One-line pitch + bash install.
  2. Hello-agent code block (load-bearing teaser).
  3. `What you get` table — every row links to the matching concept page on the website.
  4. `The agent loop` (one SVG + 4-bullet narration + link to the architecture page).
  5. `Architecture` (one SVG + 1-line caption).
  6. `Multi-agent` table (six in-process patterns + A2A).
  7. `Quick start` (12-line scheduling agent).
  8. `Tutorials` table grouped by track + 3 demo links.
  9. `Repo layout` text tree.
  10. `Contributing` (with the new `hatch run check` gate).
  11. `Citing GSAR` BibTeX block.
  12. `License` one-liner.
• README dropped 502 → 292 lines (-42%).
• Tutorial counter says `39 progressive tutorials` (was 38; matches current state after PR feat: GSAR Agent integration — Agent(gsar=GSARConfig(...)) #19).
• `Six coordination patterns plus A2A` framing throughout (matches PR docs: align multi-agent count — six in-process patterns plus A2A #7 alignment).

Drive-bys

• New `Citing GSAR` section with BibTeX block pointing at `arXiv:2604.23366` so production users / academics have a clean citation handle.
• `What you get` row links go to website concept pages, not local markdown — readers landing on GitHub now find their way into curated website content.

Test plan

• CI passes (`CI Success` aggregator: format-check + lint + mypy across Python 3.11/3.14, tests across 3.11/3.12/3.13/3.14, pre-commit, DCO).
• All links in the README resolve (the website concept pages exist; tutorial paths exist in `examples/`).