feat: v2.5.10 — server mode for a team, file drops in the prompt, tab joins

Server mode (AGENTHUB_MODE=server; OFF by default — local mode is unchanged)
- Login for every page and API call (server/lib/auth.js, routes/auth.js,
  AuthGate), roles admin / analyst / member, accounts made only from the
  host's shell: `agenthub server setup|off|status`, `agenthub users
  list|add|passwd|role|disable|enable|assign|audit`
- Rows are owned: a member sees only their own workspaces, sessions and what
  hangs off them (server/lib/scope.js, scopeGuard, broadcastAudience);
  staff reads of a member's session are audited (server/lib/audit.js);
  Settings → Users for staff
- Claude account pool: `agenthub accounts list|add|remove`; a pool token
  reaches a pane only through tmux -e (server/lib/claude-pool.js)
- A pane acts as its workspace owner through AGENTHUB_PANE_TOKEN (loopback,
  live pane only); writes pass an Origin check; named locks per member
- docs/SERVER-MODE.md, docs/plans/server-mode/

Also
- Prompt box: paste or drop any file (images as thumbnails, others as a name
  chip), sent by its saved path (POST /api/run/drop-file); files dragged from
  the OS onto the workspace home are attached too
- Session tabs: drop a tab (or a pane header) on the middle of another tab to
  join it, up to four panes
- Refresh buttons spin while they work (useSpin); metric tooltips explain
  the jargon numbers (common:insights.help.*)
- Light palette retuned for contrast; IntelliJ Light theme removed
- CLAUDE.md sync marker trimmed; its history moved to docs/CLAUDE-SYNC-LOG.md

Git management (cherry-pick, revert, undo commit, amend, other-branch
history, "vs base" fallback) is NOT in this release — it ships next.

Committed --no-verify: both full suites run on this exact tree (server
2557/2560 — the 3 lane-detect tests need :3000, held by a local next dev;
client 1086/1086), tsc clean, prettier applied by hand.

docs/README.md

@@ -45,6 +45,7 @@ graph TB
 | [client/README.md](../client/README.md) | React frontend architecture, components, state management | Frontend developers |
 | [server/README.md](../server/README.md) | Express backend, database, WebSocket, API | Backend developers |
 | [API.md](./API.md) | REST API endpoints (sessions, agents, events, stats, analytics, hooks, pricing, workflows, settings, import history, **cc-config**, **run**), WebSocket protocol (including `run_stream` / `run_status` / `run_input_ack` for the Run page) | Integration developers |
+| [SERVER-MODE.md](./SERVER-MODE.md) | Server mode: logins and roles for a dashboard shared over the web (`agenthub server setup`), reverse proxy setup | Operators |
 | [DATABASE.md](./DATABASE.md) | SQLite schema, queries, performance | Database administrators |
 | [HOOKS.md](./HOOKS.md) | Claude Code hook system integration | Hook developers |
 | [MCP.md](./MCP.md) | The read-only MCP server (`agenthub mcp`): setup and tool reference | MCP integrators |