Add theme tokens for assistant prose and tool output

Currently, the custom theme system exposes ~69 color tokens but none of them control:

• Claude's response prose (the assistant's markdown output)
• Tool output / tool-result display

Both fall through to the terminal's default foreground color, with no way to recolor them via a custom theme. Verified this by setting every documented token to a distinct color and confirming both regions remained at terminal default.

This makes verbose mode ("verbose": true) hard to scan — tool calls, tool results, and Claude's prose all render in the same color, blending together visually.

It's also surprising given that:

• User messages can be styled (briefLabelYou, userMessageBackground)
• Subagents each get their own color (*_FOR_SUBAGENTS_ONLY)
• But Claude prime's prose has no token at all

Request: expose theme tokens such as assistantProseText (or similar) and toolOutputText / toolResultText so users can give these regions a distinct color in ~/.claude/themes/<name>.json.

Version: Claude Code 2.1.146
Docs reference: https://code.claude.com/docs/en/terminal-config#create-a-custom-theme