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/lanes/LaneConflictView.tsx

@@ -38,6 +38,7 @@ function Lines({ lines, className = "" }: { lines: string[]; className?: string
 export function LaneConflictView({
   laneId,
   session,
+  source,
   path,
   onResolved,
   onEdit,
@@ -45,6 +46,8 @@ export function LaneConflictView({
   laneId: number;
   /** Work in that session's own worktree (see `gitTarget`). */
   session?: string;
+  /** Work in that extra folder's repo instead (`lane_sources` id, see `gitTarget`). */
+  source?: number;
   path: string;
   /** The file left the conflict (resolved, or a whole side taken). */
   onResolved: () => void;
@@ -65,7 +68,7 @@ export function LaneConflictView({
     setChoices([]);
     setError(null);
     api.lanes
-      .gitFile(gitTarget(laneId, session), path, "work")
+      .gitFile(gitTarget(laneId, session, source), path, "work")
       .then((r) => {
         if (!live) return;
         setFile(
@@ -78,7 +81,7 @@ export function LaneConflictView({
     return () => {
       live = false;
     };
-  }, [laneId, session, path]);
+  }, [laneId, session, source, path]);
 
   const parts: ConflictPart[] | null = file?.usable ? parseConflicts(file.lines) : null;
   const total = parts ? parts.filter((p) => p.kind === "conflict").length : 0;
@@ -102,15 +105,18 @@ export function LaneConflictView({
     run(async () => {
       if (!parts || !file?.sha) return;
       await api.lanes.gitSaveFile(
-        gitTarget(laneId, session),
+        gitTarget(laneId, session, source),
         path,
         applyChoices(parts, choices).join("\n"),
         file.sha
       );
-      await api.lanes.gitAction(gitTarget(laneId, session), "resolve", { path, side: "done" });
+      await api.lanes.gitAction(gitTarget(laneId, session, source), "resolve", {
+        path,
+        side: "done",
+      });
     });
   const takeAll = (side: "ours" | "theirs") =>
-    run(() => api.lanes.gitAction(gitTarget(laneId, session), "resolve", { path, side }));
+    run(() => api.lanes.gitAction(gitTarget(laneId, session, source), "resolve", { path, side }));
 
   const choose = (i: number, c: ConflictChoice | undefined) =>
     setChoices((prev) => {