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/StatCard.tsx

@@ -77,6 +77,8 @@ interface StatCardProps {
   loading?: boolean;
   /** Drill-in: the whole card links here (e.g. the list the number counts). */
   to?: string;
+  /** Plain-language explanation of the metric, shown as the label's tooltip. */
+  help?: string;
 }
 
 /**
@@ -92,11 +94,15 @@ export function StatCard({
   raw,
   loading = false,
   to,
+  help,
 }: StatCardProps) {
   const body = (
     <>
       <div className="flex items-center justify-between gap-3 mb-3">
-        <span className="text-xs font-medium text-fg-muted uppercase tracking-wider truncate">
+        <span
+          className={`text-xs font-medium text-fg-muted uppercase tracking-wider truncate${help ? " cursor-help underline decoration-dotted underline-offset-2" : ""}`}
+          title={help}
+        >
           {label}
         </span>
         <Icon className={`w-5 h-5 flex-shrink-0 ${accentColor}`} />