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.

server/openapi-extra/lanes.js

@@ -715,11 +715,12 @@ const paths = {
       tags: ["Lanes"],
       summary: "Suggest a commit message for the staged changes",
       description:
-        "Runs the user's `claude` CLI (`-p --safe-mode --no-session-persistence --tools \"\" --model haiku`) on the STAGED diff of the lane's cwd (or `?session=` worktree), sent on stdin with the last ten commit subjects; a `settings.local.json` is never included. Reads only — nothing is staged or committed, no tool runs and no session is saved. Same-origin, since each call spends the user's Claude quota. 400 ENOSTAGED when nothing is staged, 400 ENOTOOL when `claude` is not on PATH, 502 EAI when the CLI fails, answers empty or runs past 120 s.",
+        "Runs the user's `claude` CLI (`-p --safe-mode --no-session-persistence --tools \"\" --model haiku`) on the STAGED diff of the lane's cwd (or `?session=` worktree, or `?source=` extra folder), sent on stdin with the last ten commit subjects; a `settings.local.json` is never included. Reads only — nothing is staged or committed, no tool runs and no session is saved. Same-origin, since each call spends the user's Claude quota. 400 ENOSTAGED when nothing is staged, 400 ENOTOOL when `claude` is not on PATH, 502 EAI when the CLI fails, answers empty or runs past 120 s.",
       operationId: "suggestLaneCommitMessage",
       parameters: [
         { name: "id", in: "path", required: true, schema: { type: "integer" } },
         { name: "session", in: "query", required: false, schema: { type: "string" } },
+        { name: "source", in: "query", required: false, schema: { type: "integer" } },
       ],
       responses: {
         200: {
@@ -736,7 +737,7 @@ const paths = {
         },
         400: { description: "ENOSTAGED / ENOTOOL / ENOWORKTREE" },
         403: { description: "Cross-origin request refused" },
-        404: { description: "No such workspace" },
+        404: { description: "No such workspace, or ENOSOURCE" },
         502: { description: "EAI — the claude CLI failed" },
       },
     },