feat: account pool per tool with groups and a Cursor pool; update runs in the background

- The update dialog can be closed while an update applies: it keeps running,
  the page still reloads itself when the new server is up, and a failure
  re-opens the dialog with its error.
- Account pool card: one tab per AI tool (Claude Code, Codex, Cursor CLI,
  Oh My Pi, and every other installed tool, which says it has no pool),
  accounts as cards with 5-hour and weekly quota shown as what is LEFT plus
  their reset times, and the saved profiles of Settings → AI tools →
  Profiles as cards with "Share to pool".
- Cursor account pool (server/lib/cursor-pool.js): Cursor API keys handed to
  a cursor-agent pane only through tmux -e CURSOR_API_KEY;
  `agenthub accounts add <name> --tool cursor`.
- Pool groups (server/lib/pool-groups.js, /api/accounts/groups): a group's
  members run only on its accounts of each tool, a user in no group on the
  accounts no group lists, a pin still wins. account_pins loses its tool
  CHECK (rebuilt, pins kept); three new tables.
- Oh My Pi login sharing can be switched from its pool tab too.

docs/SERVER-MODE.md

@@ -535,12 +535,62 @@ 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.
 
+## Cursor account pool
+
+Cursor CLI sessions get a pool too (`server/lib/cursor-pool.js`): Cursor API
+keys (Cursor dashboard → Integrations → API keys), added on the Users page's
+**Account pool → Cursor CLI** tab or from the shell:
+
+```bash
+agenthub accounts add cursor-team --tool cursor   # key typed hidden, or piped on stdin
+agenthub accounts list --tool cursor
+agenthub accounts remove cursor-team --tool cursor
+agenthub accounts pin cursor-team mia --tool cursor
+```
+
+- The key reaches the pane only as tmux `-e CURSOR_API_KEY=…` (a member's
+  launch file under S3), which `cursor-agent` prefers over the account's own
+  `cursor-agent login` for that process only. Nothing is written into a home.
+- Cursor reports no usage or quota to AgentHub, so the account with the fewest
+  live Cursor panes is picked.
+
+> **Ceiling:** a pane can read its own key (`$CURSOR_API_KEY`).
+
+## Account pool groups
+
+By default every user shares every pool account. **Groups** split the pool
+by team (Users page → **Account pool → Groups**, server mode only,
+`server/lib/pool-groups.js`):
+
+- A group has a name, members and accounts of every pool tool (Claude, Codex,
+  Cursor). Its members' new sessions run only on its accounts of that tool; a
+  group with no account of a tool leaves its members on their own sign-in.
+- A user belongs to at most one group (ticking them in another moves them).
+  An account may serve several groups.
+- A user in no group runs on the **shared pool**: the accounts no group lists.
+  With no group at all, everything is shared, as before.
+- A pin (Edit on an account) is an admin's explicit choice and wins over the
+  group.
+- A login already live in a member's home stays until their panes end (one
+  `.credentials.json` / `auth.json` per home), even after a group change.
+- Each change needs the admin's own password again and is audited. Removing
+  an account takes it out of every group; deleting a group sends its members
+  back to the shared pool and removes no account.
+
+The tab bar also shows Oh My Pi (its login sharing, below) and every other
+installed tool, which says it has no pool (Antigravity keeps its Google login
+in the system keyring; there is no key AgentHub could hand a session).
+
+The Claude and Codex tabs list the saved profiles of Settings → AI tools →
+Profiles as cards; **Share to pool** moves one in (the profile leaves the
+switcher, as with **Move to pool** in Settings).
+
 ## 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
+logins instead: **Settings → AI tools → Oh My Pi login sharing**, or the
+**Oh My Pi** tab of the Users page's Account pool (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