feat: add claude-fable-5 to model registry

[sanchitmehtagit]

What

Registers claude-fable-5 across all model registry locations.

Files changed:

• packages/eval-core/src/config/costs.ts — adds pricing [10.0, 50.0] ($10/M input, $50/M output)
• packages/eval-core/src/config/settings.ts — adds claude-fable-5 to CLAUDE_EFFORT_MODELS
• packages/eval/src/cli/constants.ts — adds claude-fable-5 to KNOWN_WORKING_MODELS (included in --model all runs)
• apps/auth0-evals/eval.config.js — adds claude-fable-5 to models.known and maps the alias to global.anthropic.claude-fable-5 in the Bedrock modelIds map

Why

Adds claude-fable-5 so it can be targeted with --model claude-fable-5 and included in --model all runs across all eval configurations.