/admin shows today's peak viewers and joins per hour for the last 24 h, owner only, kept under FORGE_APP_DATA across a restart #374

Replaces #366, which was parked only because it inherited a blocker on #291 (closed as split). This one waits only on what it names. Rewritten from #293, piece 2 of 2.

Done:

• [ ] The lobby feeds one VisitorCounts on every /live connect and disconnect and saves it under FORGE_APP_DATA at most once a minute and on close.
• [ ] src/admin-page.ts renders the peak and a 24-bar text or CSS chart (no script) for the owner. Anyone else gets the existing refusal.
• [ ] Tests: the owner sees the counts, a moderator and a plain user do not, and the counts survive a relay restart.
• [ ] forge.json untouched, and bun --cwd Software/so101 test passes.

duplicate of #366