feat: add interactive 2-user lab environment + fix requirements.txt encoding

- lab/setup-lab.sh: automated tmux setup with server + 2 chat clients
  Supports --no-tls, --password, --port, --user1/--user2, --teardown
  Auto-installs missing pip dependencies, verifies port availability,
  waits for server health before connecting clients
- lab/README.md: usage docs and keyboard shortcuts
- requirements.txt: fixed UTF-16 encoding to UTF-8, cleaned pinned versions

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lab/README.md

@@ -0,0 +1,55 @@
+# cmd-chat Lab
+
+Interactive 2-user test environment using tmux. Spins up a server and two chat clients side-by-side so you can send messages between them.
+
+## Quick Start
+
+```bash
+# Default (TLS, password: labtest)
+./lab/setup-lab.sh
+
+# Plain HTTP (local testing)
+./lab/setup-lab.sh --no-tls
+
+# Custom password and port
+./lab/setup-lab.sh --password mysecret --port 5000
+
+# Custom usernames
+./lab/setup-lab.sh --user1 charlie --user2 dave
+```
+
+## Attach & Navigate
+
+```bash
+tmux attach -t cmd-chat-lab
+```
+
+| Key | Action |
+|-----|--------|
+| `Ctrl+B` then arrow keys | Switch between panes |
+| `Ctrl+B` then `z` | Zoom/unzoom current pane |
+| `q` | Disconnect from chat |
+| `Ctrl+C` in server pane | Stop server |
+
+## Teardown
+
+```bash
+./lab/setup-lab.sh --teardown
+```
+
+## Layout
+
+```
+┌──────────── SERVER (127.0.0.1:4000) ─────────────┐
+│ Sanic running, admin token displayed here        │
+├──────── alice ───────┬──────── bob ──────────────┤
+│ Type messages here   │ Type messages here        │
+│ and hit Enter        │ and hit Enter             │
+└──────────────────────┴───────────────────────────┘
+```
+
+## Requirements
+
+- Python 3.10+
+- tmux 3.0+
+- All Python deps from `requirements.txt` (auto-installed if missing)