Lean README + CONFIGURATION.md split, demo polish (SF Mono, model switch)

[FrancoisChastel]

Summary

Docs

• README.md is now ~70 lines: a clean landing page focused on first install — 3 steps with the local model, the five glyphs, and 5 example moves worth knowing. Everything else is one link out.
• CONFIGURATION.md (new) carries the deep reference that used to bloat the README: model tiers, sessions, terminal-context ladder, semantic recall, claude-mem, the hard wall, the full env-var table, hosted-API setup, JS rendering, what's deliberately not built.
• AGENTS.md gains a contributor quickstart at the top (clone → venv → test → ruff).

Demo polish

• Font → SF Mono so the gif matches macOS Terminal/iTerm defaults out of the box (was JetBrainsMono Nerd Font, which most users don't have installed).
• Failed command upgraded from gti status (one-letter swap, too obviously a setup) to git log --oneline -n 10 --grpe 'fix' — the kind of flag typo a developer actually makes mid-flow.
• Per-call model routing shown explicitly: , --fast, ,, --fast, ? --fast for the cheap turns; ? --balanced for the harder diagnosis of the piped Python traceback. The visible tier flags make the side-by-side routing pillar self-explanatory without needing the docs.
• ,, zsh function now accepts a leading tier flag so ,, --fast routes the fix call (previously the flag was eaten by the ctx-vs-fix switch).
• Both tiers warmed in the hidden setup so cold-start latency doesn't bleed into the visible beats.

Test plan

• 257 tests pass (`pytest -q`)
• `ruff check` and `ruff format --check` clean
• Demo renders end-to-end with a live local model; all beats land cleanly (verified frame-by-frame)
• Visual: docs render correctly on GitHub — README hero gif loads, anchor links into CONFIGURATION.md work