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.

server/__tests__/run.test.js

@@ -248,4 +248,29 @@ describe("POST /api/run/drop-image", () => {
     });
     assert.equal(r.status, 403);
   });
+
+  it("drop-file saves any file under a random prefix and its sanitized name", async () => {
+    const name = encodeURIComponent("../../báo cáo Q3.pdf");
+    const r = await fetchJson(`/api/run/drop-file?name=${name}`, {
+      method: "POST",
+      raw: { type: "application/pdf", buf: Buffer.from("%PDF") },
+    });
+    assert.equal(r.status, 200);
+    assert.equal(
+      path.dirname(r.body.path),
+      path.join(os.tmpdir(), `agenthub-drops-${os.userInfo().uid}`)
+    );
+    assert.match(path.basename(r.body.path), /^[0-9a-f]{16}-b_o_c_o_Q3\.pdf$/);
+    assert.equal(fs.readFileSync(r.body.path, "utf8"), "%PDF");
+    assert.equal(fs.statSync(r.body.path).mode & 0o777, 0o600);
+    fs.unlinkSync(r.body.path);
+  });
+
+  it("drop-file without a name or a body is refused", async () => {
+    const r = await fetchJson("/api/run/drop-file", {
+      method: "POST",
+      raw: { type: "text/plain", buf: Buffer.alloc(0) },
+    });
+    assert.equal(r.status, 400);
+  });
 });