feat(discord): per-channel CLAUDE.md and skill overrides

[TerrysPOV]

Background

Per-channel session isolation is already implemented — each Discord channel gets its own Claude conversation. This issue extends that to allow different behaviour per channel: different CLAUDE.md content, different enabled skills, different prompt prefixes.

Use cases

• A #code-review channel that has a strict reviewer persona and code-specific skills enabled
• A #research channel with web search skills and a different system prompt
• A #personal channel with a casual tone and memory tools enabled
• Running effectively different "agents" in different channels of the same Discord server

Proposed config

{
  "discord": {
    "channels": {
      "1234567890": {
        "claudeMd": "./channels/code-review/CLAUDE.md",
        "skills": ["code-reviewer", "security-review"],
        "systemPromptPrefix": "You are a senior code reviewer..."
      }
    }
  }
}

Falls back to global config for unconfigured channels.

Why ClaudeClaw-Plus

• Extends the per-channel session infrastructure already in Plus
• The agent configuration system (agents/, per-agent CLAUDE.md) already exists in Plus and can be reused

Source

Requested by @zodo in moazbuilds/claudeclaw#14 (Mega-Post).