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/SERVER-MODE.md

@@ -155,6 +155,10 @@ Workspaces made before server mode, or by the host account, have none.
 - An **admin** or **analyst** sees everything. Each time one of them opens a
   session a developer owns (its page, transcript, events or cost), the read is
   written to the audit log: `agenthub users audit`, or `GET /api/users/audit`.
+  Entries are kept `AGENTHUB_AUDIT_DAYS` days (default 180; `0` keeps them
+  all) — older ones are deleted as new ones are written, at most once an hour.
+  An account's last login is kept in `users.last_login_at`, so it still shows
+  after the login itself has ended.
 - `GET /api/users` (admin/analyst) lists every account with its workspaces,
   sessions, and the tokens and $ it used in the last 7 and 30 days — the
   **Administration** page in the sidebar (`/admin`; the old `/users` link
@@ -264,7 +268,22 @@ settings file that lacks the variable falls back to `USERS_ROOT` in
 - A login lasts 30 days in the httpOnly, `SameSite=Strict` cookie
   `agenthub_sid`. Only the token's SHA-256 is stored. Logging out, a password
   change and disabling the user each end it.
-- Passwords are stored as scrypt hashes; any non-empty password is accepted (no minimum length).
+- Passwords are stored as scrypt hashes. Two bars:
+  - A password an admin **gives** someone — **Add user**, a reset on the Edit
+    form, `agenthub users add` — may be anything non-empty (`123` included).
+    The account is then flagged `must_change_password`: after signing in it
+    sees only a "Choose your own password" page, the server answers every
+    other request with `403 EPWCHANGE` (only `/auth/*`, the `/me` reads and
+    `POST /api/me/password` pass) and no WebSocket opens. A pane token is not
+    held back — agents started before a reset keep running.
+  - A password an account **picks for itself** (that page, Settings → Account,
+    an admin's own on the Edit form) must pass every rule: at least 8
+    characters, a lower-case and an upper-case letter, a digit, a symbol, not
+    containing the username, and not the current password (`400
+    EWEAKPASSWORD`, with the failed `rules`). The form ticks each rule as it is
+    typed (`client/src/lib/passwordRules.ts` mirrors `passwordProblems` in
+    `server/lib/auth.js`). `agenthub users passwd` and the first admin of
+    `agenthub server setup` set no flag.
   Every login attempt counts before its password is checked, so attempts sent
   in parallel count too. After 10 failed logins from one address, or 30 for one
   username, in 15 minutes, further logins answer `429 ETOOMANY` until the
@@ -307,7 +326,10 @@ everywhere". Every field is checked before any is written, so a bad email or
 a workspace the user does not own changes nothing. Every change asks for the admin's OWN
 password again — the server refuses without it (`EREAUTH`, and `ETOOMANY`
 after 10 wrong tries in 15 minutes) — an admin can never demote or disable
-themselves (`ESELF`), and each change is written to the audit log. In local
+themselves (`ESELF`), no path (the CLI included) may demote, disable or
+delete the last enabled admin (`ELASTADMIN`), and each change is written to
+the audit log. A row says **New password due** while the account still has a
+password an admin gave. In local
 mode these routes refuse (`ELOCALMODE`): there is no login to check.
 
 Wherever the dashboard names a person — the sidebar's sign-out tooltip, the
@@ -335,10 +357,10 @@ The same from the host's shell:
 
 ```bash
 agenthub users list
-agenthub users add <name> [--role admin|analyst|developer]
+agenthub users add <name> [--role admin|analyst|developer]   # they choose their own password at first login
 agenthub users passwd <name>        # ends that user's logins
-agenthub users role <name> <role>
-agenthub users disable <name>       # ends that user's logins; users are never deleted
+agenthub users role <name> <role>   # never the last enabled admin (ELASTADMIN)
+agenthub users disable <name>       # ends that user's logins; never the last enabled admin
 agenthub users enable <name>
 agenthub users assign <workspace id> <name>   # give a pre-server-mode workspace an owner
 agenthub users audit [--limit N]    # who read which developer's session
@@ -507,6 +529,48 @@ agenthub accounts pin team-key mia --tool codex   # pins work as for Claude
 > **Ceiling:** a pane can read its own account's key (`$AGENTHUB_POOL_KEY`) or
 > `auth.json`, like the Claude pool's token.
 
+## Oh My Pi login sharing
+
+With one Linux user per account, a member's omp has its own `~/.omp` and no
+login. An admin can let every member's omp run on the HOST account's omp
+logins instead: **Settings → AI tools → Oh My Pi login sharing** (off by
+default; `PUT /api/ai-tools/omp-sharing`, audited). It uses omp's own auth
+broker and gateway (`server/lib/omp-share.js`):
+
+```bash
+# as the host account: the logins to share (omp's built-in providers only)
+omp login            # e.g. anthropic
+```
+
+- While it is on, the dashboard runs, as the host and on loopback only,
+  `omp auth-broker serve --bind=127.0.0.1:4826` over the host's `~/.omp` store
+  and `omp auth-gateway serve --bind=127.0.0.1:4827 --clients=<data dir>/omp-share/clients.json`
+  (ports: `AGENTHUB_OMP_BROKER_PORT`, `AGENTHUB_OMP_GATEWAY_PORT`; logs in
+  `<data dir>/omp-share/`). Both tokens stay in the host's 0700 home; the
+  broker's reaches only the gateway's env. A crashed daemon restarts with a
+  back-off; the server stops both on shutdown, and kills ones a previous
+  server left (by pid file and argv) before starting its own.
+- A member's omp pane gets one provider `agenthub` in its
+  `~/.omp/agent/models.yml` (written as the member; the rest of the file is
+  kept, a file that is not a YAML mapping is left alone), pointing at the
+  gateway with `apiKey: AGENTHUB_PANE_TOKEN` — the NAME of the env var holding
+  its pane token — and `OMP_SKIP_SETUP=1`. It runs on `--model agenthub/<model>`:
+  the model picked in AgentHub, else the host's own `modelRoles.default`
+  (`~/.omp/agent/config.yml`) — left to itself omp would take the provider's
+  first listed model, a retired one the API answers 404 for. The clients file lists the SHA-256
+  of each LIVE omp pane's token (rewritten every 15 s; the gateway re-reads it
+  every 10 s), so a token stops working shortly after its pane ends, and
+  turning sharing off empties it at once.
+- A scoped client token calls models only: it cannot read a credential, the
+  gateway's usage or credential health, and refresh tokens never leave the
+  broker. Host panes use the host's login directly and get nothing new.
+- A custom provider in the host's own `models.yml` (a 9Router, say) is not
+  shared — the gateway serves omp's built-in providers.
+
+> **Ceiling:** an agent can SPEND through the shared logins while its pane
+> runs; it cannot carry a login away. A member who edits the `agenthub`
+> provider out of their `models.yml` gets it back at their next omp pane.
+
 ## One Linux user per account
 
 Every pane of a user, an agent's shell included, runs as that user's own Linux