Document and test Fable model support

[medking82]

Summary

• document Fable as an explicit --model fable option across the README, bundled Skill, and CLI help
• preserve the existing pass-through model contract so full model names and future Claude Code aliases continue to work
• filter the Fable startup banner from monitor progress and add foreground/background argument-builder coverage

Why

The companion runtime already forwards arbitrary explicit model values to Claude Code, but the public guidance only presented Sonnet and Opus and the monitor banner filter did not recognize Fable. This makes Fable first-class without changing the configured default or adding a local model allowlist.

Behavior

Fable remains explicit opt-in. Existing read-only, prepared-task, MCP, web, and --write boundaries are unchanged. Availability is resolved by the installed Claude Code CLI and account.

Validation

• npm run validate
• npm run test:smoke
• python3 .../skill-creator/scripts/quick_validate.py plugins/claude-code-advisor/skills/claude
• python3 .../plugin-creator/scripts/validate_plugin.py plugins/claude-code-advisor
• git diff --check

npm run test:e2e:codex was not run because it requires installing the plugin into the user's Codex configuration and performs a live Sonnet request. The deterministic routing tests cover --model fable in both foreground and background argument builders.