feat: v2.6.0 — Chat UI composer (+ menu, project files, activity panel, permission mode, Stop), git on a workspace's extra folders (#70), long paste as a file (#68), S3 server mode (experimental)

Chat UI:
- Each Claude/Codex session keeps its own chat/terminal view; Settings only
  sets how new sessions open.
- Composer + menu: upload, project files and folders (#54, also dragged from
  the Files/Changes tree), context files, recent uploads, skills, plugins.
- Activity side panel (progress, outputs, files read, uploads, memory,
  skills, connectors) with a file preview; edited-file counts per turn.
- Permission-mode chip (Shift+Tab steps, read back from the pane:
  server/lib/pane-mode.js, GET|POST /api/run/:id/permission-mode).
- Stop (Esc) while the main agent works; the status is checked per agent
  (with session_id /api/agents ignores its status filter) and re-read every
  5 s while Stop shows.
- Dropped images shown in the conversation (GET /api/run/drop/:name, the
  requester's own drop dir), full-size viewer.
- A plain-text paste over 5,000 characters is attached as pasted-text.txt,
  so no prompt reaches tmux/argv limits (#68).

Changes panel: every /api/lanes/:id/git* route takes ?source=<lane_sources
id> (sourceFolder; ENOSOURCE otherwise) and a folder picker switches the
whole panel to a workspace's extra folder (#70).

Server mode S3 (one Linux user per account) — experimental, verified with
fake sudo plus a P6 managed-settings spike on a test account:
- member tmux listing runs in the background (cached, 15 s => unknown);
- transcript snapshot copy is async, chunked, temp file + rename;
- Express Layer patch only on Express 4;
- tmux capturePane/sendKey go to the member's own server.

Docs: the multi-user design moved in as docs/plans/server-mode/README.md
(the AgentHub-Server repo is gone); S3-PLAN P6 result; LANES/API/openapi.

client/src/components/run/__tests__/ChatFilePreview.test.tsx

@@ -0,0 +1,78 @@
+/**
+ * @file ChatFilePreview.test.tsx
+ * @description Where a Chat pane's file preview reads from: a file under the
+ * pane's folder through the lane's git file read, a memory file under
+ * `~/.claude` through the config pages' read, anything else by path only; and
+ * the list dialog previewing the file picked in it.
+ * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
+ */
+
+import { fireEvent, render, screen } from "@testing-library/react";
+import { describe, expect, it, vi } from "vitest";
+import { FileListModal, FilePreview, displayName } from "../ChatFilePreview";
+import { api } from "../../../lib/api";
+
+vi.mock("../../../lib/api", async (importOriginal) => {
+  const actual = await importOriginal<Record<string, unknown>>();
+  return {
+    ...actual,
+    api: {
+      lanes: {
+        gitFile: vi.fn().mockResolvedValue({
+          available: true,
+          path: "src/a.ts",
+          rev: "work",
+          binary: false,
+          truncated: false,
+          lines: ["export const a = 1;"],
+        }),
+        gitRawUrl: () => "",
+      },
+      ccConfig: {
+        file: vi
+          .fn()
+          .mockResolvedValue({ ok: true, file: "", text: "Launch notes", size: 12, mtime: 0 }),
+      },
+    },
+  };
+});
+
+const scope = { laneId: 4, laneCwd: "/w", cwd: "/w", sessionId: "s1" };
+
+describe("FilePreview", () => {
+  it("reads a workspace file through the lane", async () => {
+    render(<FilePreview path="/w/src/a.ts" scope={scope} onClose={() => {}} />);
+    expect(await screen.findByText("export const a = 1;")).toBeTruthy();
+    expect(vi.mocked(api.lanes.gitFile)).toHaveBeenCalledWith(4, "src/a.ts");
+  });
+
+  it("reads a memory file through the config read", async () => {
+    const mem = "/h/.claude/projects/-w/memory/launch.md";
+    render(<FilePreview path={mem} scope={scope} onClose={() => {}} />);
+    expect(await screen.findByText("Launch notes")).toBeTruthy();
+    expect(vi.mocked(api.ccConfig.file)).toHaveBeenCalledWith(mem);
+  });
+
+  it("shows only the path of a file it may not read", () => {
+    render(<FilePreview path="/etc/hosts" scope={scope} onClose={() => {}} />);
+    expect(screen.getByText("No preview for this file here")).toBeTruthy();
+  });
+});
+
+describe("FileListModal", () => {
+  it("previews the file picked in the list", async () => {
+    const drop = "/tmp/agenthub-drops-1000/0123456789abcdef-minutes.xlsx";
+    expect(displayName(drop)).toBe("minutes.xlsx");
+    render(
+      <FileListModal
+        title="Uploads"
+        paths={[drop, "/w/src/a.ts"]}
+        scope={scope}
+        onClose={() => {}}
+      />
+    );
+    expect(screen.getByText("No preview for this file here")).toBeTruthy();
+    fireEvent.click(screen.getByRole("button", { name: "a.ts" }));
+    expect(await screen.findByText("export const a = 1;")).toBeTruthy();
+  });
+});