- Add support for sk-{key}:{channelId} format to specify channel dynamically
- Remove BoundChannelId field and related code
- All users can now specify channels, not just admins
- Add model validation when channel is specified
- Remove bound channel UI from token management

Breaking change: tokens can no longer be bound to channels at creation time.
Use sk-{key}:{channelId} format instead.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

This PR fixes three issues:
1. Token bound_channel_id not updating: Add bound field to Update() method
2. Channel pricing quota_type detection: Use QuotaTypeByCall constant instead of magic number 1
3. Log display for ratio-based pricing: Set ModelPrice=-1 for ratio-based pricing

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Add BoundChannelId field to support binding a token to a specific channel.
When set, the token will always use the bound channel for requests.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>