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.

docs/DATABASE.md

@@ -625,7 +625,7 @@ Server mode's accounts ([SERVER-MODE.md](SERVER-MODE.md), `server/lib/auth.js`).
 
 `dashboard_runs.account` names the Claude pool account a run's pane was started on (`server/lib/claude-pool.js`; `NULL` = the machine's own login). The balancer sums each account's spend from the `token_usage_hourly` rows of those runs' sessions. The pool's tokens live in files under `<CLAUDE_HOME>/agenthub-accounts/`, never in the database.
 
-`lanes.owner_id` (server mode) is the user who created a workspace; `NULL` for one made in local mode or by the host account. A member sees only sessions of their own workspaces, and everything hanging off them (`server/lib/scope.js`). `audit_log` (`user_id`, `owner_id`, `session_id`, `method`, `path`, `at`) records each admin/analyst read of a session a member owns.
+`lanes.owner_id` (server mode) is the user who created a workspace; `NULL` for one made in local mode or by the host account. A member sees only sessions of their own workspaces, and everything hanging off them (`server/lib/scope.js`). `audit_log` (`user_id`, `owner_id`, `session_id`, `method`, `path`, `at`) records each admin/analyst read of a session a member owns, and each admin account change; rows older than `AGENTHUB_AUDIT_DAYS` (default 180) are pruned as new ones are written. `users.last_login_at` is the account's last login (kept past its `auth_sessions` row); `users.must_change_password` (0/1) is set when an admin gives the password (create, reset) and cleared when the account picks its own.
 
 `dashboard_runs.pane_token_hash` is the SHA-256 of the pane credential (`AGENTHUB_PANE_TOKEN`) a server-mode pane was started with; it is never returned by any route. `push_subscriptions.user_id` is the user whose browser a subscription is (`NULL` in local mode).