chore: v2.8.13 — Artifacts reinstall/edit/installs, agent steps in chat, pick a local file to attach, Windows paths as links

- Chat: an Agent step shows its task, status and tool calls and opens its conversation in place; Windows paths (E:\…, C:/…) in replies open as files
- Prompt: attach a file on this computer by path (native picker), clearer too-large messages
- Artifacts: edit title/description and a skill's files (new snapshot), Reinstall, install history, Hub-only rows, skills installed into ~/.claude/skills and ~/.agents/skills
- Files: batch upload of small files in one extract
- AI Tools: npm install falls back to --prefix ~/.local when the global prefix is not writable

docs/SERVER-MODE.md

@@ -63,7 +63,10 @@ The proxy has to:
 - pass the original `Host` (the dashboard checks it against
   `DASHBOARD_ALLOWED_HOSTS` and compares it with the browser's `Origin`);
 - forward WebSocket upgrades (`/ws` for live updates, `/ws-pty/*` for terminals);
-- set `X-Forwarded-For` and `X-Forwarded-Proto`.
+- set `X-Forwarded-For` and `X-Forwarded-Proto`;
+- accept request bodies as large as AgentHub's own limits (Files uploads up to
+  500 MB, prompt drops 20 MB). nginx's default `client_max_body_size` is 1 MB,
+  and its own 413 is an HTML page the UI can only report as a failed upload.
 
 nginx:
 
@@ -83,6 +86,7 @@ server {
     proxy_set_header Upgrade $http_upgrade;
     proxy_set_header Connection "upgrade";
     proxy_read_timeout 1d;
+    client_max_body_size 500m;
   }
 }
 ```
@@ -594,7 +598,7 @@ The pieces, and what each is for (the install steps are in the
 | `agenthub.service` | A SYSTEM unit, `User=<host>`, with `SupplementaryGroups=agenthub agenthub-proc` and `AmbientCapabilities=CAP_DAC_READ_SEARCH`: the dashboard can read every member's tool files (Claude writes transcripts `0600`), but cannot write them. Every program it starts has the capability removed first (`setpriv`), so host panes, git and npm do not inherit it. It reads node and the plugin root from `<data dir>/runtime/agenthub.system.env`, a file the host owns, so a plugin update repoints it without root |
 | `/etc/sudoers.d/agenthub` | The host may run only `tmux`, `git`, `gh` (by the absolute paths recorded in `/etc/agenthub/server.conf`), `/opt/agenthub/libexec/tmux-member`, `/opt/agenthub/libexec/write-as` and `/opt/agenthub/tools/bin/claude` (the [plugin baseline](#plugin-baseline-opt-in)) AS a member, plus, as root, only `/opt/agenthub/sbin/agenthub-provision` and `systemctl start/stop/restart/enable/disable agenthub.service`. Members are never in sudoers |
 | `/etc/agenthub/server.conf` | Root's, `0644`: the host account and uid, the users root, the port, and the `tmux`/`git`/`gh` paths sudoers lists. Its presence turns S3 on |
-| `write-as`, `pane-launch`, `tmux-member` | `/opt/agenthub/libexec/`, root's. `tmux-member -S <socket> …` runs a member's tmux call with their running server's own binary (else `TMUX_BIN`). `write-as <path> [append\|replace\|private\|mkdir\|remove]` runs AS a member and does the one change, content on stdin. `pane-launch <file>` starts a member's pane from its launch file |
+| `write-as`, `pane-launch`, `tmux-member` | `/opt/agenthub/libexec/`, root's. `tmux-member -S <socket> …` runs a member's tmux call with their running server's own binary (else `TMUX_BIN`). `write-as <path> [append\|replace\|private\|mkdir\|remove\|extract]` runs AS a member and does the one change, content on stdin (`extract`: a tar the dashboard wrote, unpacked with `tar -k` — the Files page's batch upload). `pane-launch <file>` starts a member's pane from its launch file |
 | `agenthub-provision` | The one root command besides `systemctl` on this unit: `create`, `disable` or `enable` `ah-<name>`. It refuses an account that exists outside `agenthub-members` and never deletes anything |
 | `/etc/claude-code/managed-settings.json` | Members' Claude Code hooks, through `/opt/agenthub/libexec/member-hook`, which does nothing for the host account (its plugin reports). A foreign file there is left alone |
 | `hidepid=invisible` | `/proc` (now and in `/etc/fstab`): an account sees only its own processes, so no member can read another's command line. A token passed with `tmux -e` is in one |