chore: v2.8.15 — Oh My Pi login sharing, omp --allow-home, Markdown Preview default, first-login password

- omp-share.js: an admin's switch (S3) runs omp's own auth broker + gateway as
  the host on loopback; a member's omp pane reaches it as a scoped client keyed
  by its pane token (clients file = live omp panes only), runs on
  --model agenthub/<model>, never holds a credential.
- omp catalog: --allow-home, so a workspace at the account's home keeps its
  sessions there (they were recorded under a temp dir and dropped).
- Settings → Appearance → Open Markdown as: Preview (default) or Raw, for
  Files/Changes, the config viewer and a chat's file panel.
- First-login password change and password rules, avatar URLs, Artifacts
  "Mine" includes installed shared skills/plugins, a member's own hook pages.

client/src/lib/userPrefs.ts

@@ -43,6 +43,7 @@ export const PREF_KEYS = [
   "agenthub.codex.bypass",
   "agenthub.tour",
   "agenthub.workspace.allTabs",
+  "agenthub.markdown.view",
 ] as const;
 const SYNCED = new Set<string>(PREF_KEYS);
 const PUSH_DELAY_MS = 400;