Create AGENTS.md, fix total-counter anchor bug, update README for repo rename, add score/roadmap

[Copilot]

Addresses three issues surfaced during repo review: stale URLs from the game → token-deathclock rename, a logic bug in the live counter, and missing AI-agent context.

Bug fix — getCurrentTokens() anchor (script.js)

The total token counter was computing elapsed time from pageLoadTime instead of the BASE_DATE_ISO data anchor, so the counter always reset to BASE_TOKENS on every page load rather than reflecting true running totals.

// Before — always starts counting from zero at page load
const elapsed = (Date.now() - pageLoadTime) / 1000;

// After — counts from the calibrated data anchor
const baseDateTime = new Date(BASE_DATE_ISO).getTime();
const elapsed = (Date.now() - baseDateTime) / 1000;

BASE_DATE_ISO is now destructured from window.DeathClockCore alongside the other constants. pageLoadTime is retained for the session counter only.

README updates

• Replaced all three occurrences of old repo name game → token-deathclock (clone URL, cd command, GitHub Pages URL).
• Added Repo Score & Roadmap section: scored 72/100 (C+) across code quality, tests, docs, CI/CD, a11y, security, bugs, and community files, with a prioritised improvement checklist.

New file — AGENTS.md

Provides AI coding agents with repo layout, architecture invariants (core/DOM split, dual-export pattern, escHtml requirement, counter anchor rule), key constants, test instructions, per-task change guides, and a prohibited-actions list.