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.

client/src/components/lanes/__tests__/WorkspaceHome.test.tsx

@@ -12,7 +12,7 @@
  */
 
 import { beforeEach, describe, expect, it, vi } from "vitest";
-import { render, screen, waitFor, within } from "@testing-library/react";
+import { fireEvent, render, screen, waitFor, within } from "@testing-library/react";
 import userEvent from "@testing-library/user-event";
 import { MemoryRouter, Route, Routes, useLocation } from "react-router-dom";
 import type { Lane, Session } from "../../../lib/types";
@@ -454,6 +454,13 @@ describe("WorkspaceHome", () => {
     const file = new File(["# notes"], "notes.md", { type: "text/markdown" });
     await user.upload(screen.getByTestId("workspace-file-input"), file);
     expect(api.lanes.addFile).toHaveBeenCalledWith(1, file);
+    const a = new File(["a"], "a.csv", { type: "text/csv" });
+    const b = new File(["b"], "b.log", { type: "" });
+    fireEvent.drop(screen.getByTestId("workspace-context-files"), {
+      dataTransfer: { types: ["Files"], files: [a, b] },
+    });
+    await waitFor(() => expect(api.lanes.addFile).toHaveBeenCalledWith(1, b));
+    expect(api.lanes.addFile).toHaveBeenCalledWith(1, a);
     await user.click(screen.getByRole("button", { name: "Remove spec.pdf" }));
     expect(api.lanes.removeSource).toHaveBeenCalledWith(1, 7);
   });