bug: Messaging bot commands with arguments (`/workspace <name>`, `/model <id>`) are never intercepted — parsed as plain chat text

Body:

Summary

Commands sent to a messaging bot (Discord/Telegram/etc.) that take an argument — /workspace <name> and /model <id> — are never intercepted by the bot's command layer. They fall through to normal message dispatch and reach the agent as plain text, so the documented behavior (/workspace <name> switches the bot's workspace and starts a new chat) never happens.

Bare commands without arguments (/new, /stop, /retry, /help, /workspaces) work fine.

Environment

• cptr version: 0.9.21 (pip package cptr, installed via venv)
• Platform: Discord bot (bug is in the shared bridge core, so it affects all platforms: Telegram, Discord, Slack, WhatsApp, Signal)
• Docs that document the command: https://docs.openwebui.com/ecosystem/computer/automate/messaging-bots/ ("Commands" table lists /workspace <name> — Switch workspace (fuzzy match) and start a new chat)

Steps to reproduce

1. Create a bot in Settings → Admin → Bots (platform: Discord, workspace: /projects), start it.
2. In the Discord channel, send: /workspace jellyfin-storage
3. Observe: no "✨ Switched to ... New conversation started." reply. Instead, the message is treated as a normal user message — the agent receives /workspace jellyfin-storage as plain text and responds to it conversationally.
4. Same result for /model <id>.

Root cause

In cptr/utils/bridge.py, BotManager._handle_message, the command is extracted like this:

# Normalize: strip Discord bot mention prefix (<@123456>)
# and Telegram command suffix (/cmd@BotName → /cmd)
import re
clean = re.sub(r"<@!?\d+>\s*", "", text).strip()
cmd = clean.split("@")[0].lower() if clean.startswith("/") else ""

clean.split("@")[0] only strips a Telegram-style @BotName suffix — it does not split on whitespace. So:

• /workspace jellyfin-storage → cmd = "/workspace jellyfin-storage" → cmd == "/workspace" is False → falls through to chat dispatch
• /model gpt-4o → cmd = "/model gpt-4o" → cmd == "/model" is False → falls through

The command handler for /workspace exists and is correct (it matches by name/path suffix, updates the bot config, and starts a new chat) — it's just unreachable because the parser never produces a bare /workspace.

Suggested fix

One line in cptr/utils/bridge.py:

cmd = clean.split()[0].split("@")[0].lower() if clean.startswith("/") else ""

Verified: this yields cmd == "/workspace" for /workspace jellyfin-storage, still strips @BotName suffixes (/cmd@BotName → /cmd), and leaves bare commands and non-slash messages unchanged.

Workaround (for users on affected versions)

Set the bot's workspace directly in Settings → Admin → Bots instead of using /workspace, or patch the single line above (note: it lives in the container's writable layer and is lost on container rebuild).

Start in cptr/utils/bridge.py at BotManager._handle_message and inspect how incoming command text is normalized before dispatch. Verify that argument-bearing /workspace and /model commands reach their handlers while bare commands, Telegram suffixes, mentions, and ordinary messages retain their existing behavior.