Minecraft platform: claim (NameMC) + modded server/client timezone display

[LizAinslie]

Parent: #810
Supersedes: #217

Goals

1. Identity claim (NameMC-shaped): join a dedicated public server → one-shot command → signed link / short-lived token on the web app. Prefer in-game token verification (HMAC/JWT) over browser Microsoft OAuth for “prove this UUID.”
2. Display: modded servers and modded clients can show known TimezoneDB timezones to users (the product outcome Minecraft/Xbox/MS Platform #217 pointed at).

Prefer

• Open comps: TheShire minecraft-player-verification; NameMC/BlockMania /namemc shape
• Fabric/Paper (or agreed loaders) for server + client surfaces — pick loaders in implementation notes

Acceptance

• Public verification server + command documented
• Web completes claim with short-lived token (replay/TTL/rate-limit notes)
• Modded server path can resolve / display a known timezone for a player
• Modded client path can display known timezones (parity scope recorded)