fix: add haiku model name translation

[weiliu2dev]

Summary

Fix translateModelName to handle Claude Haiku model variants (e.g. claude-haiku-4-5-20251001) that are not recognized by the
GitHub Copilot API.

Problem

When using Claude Code with copilot-api as a proxy, Claude Code's internal subagent calls (e.g. for codebase exploration) use the
model ID claude-haiku-4-5-20251001. This model name is sent as-is to the GitHub Copilot API, which only recognizes
claude-haiku-4.5, resulting in a 400 error:

{ message: 'The requested model is not supported.',
code: 'model_not_supported',
param: 'model',
type: 'invalid_request_error' }

The existing translateModelName function already handles claude-sonnet-4-* and claude-opus-4-* variants, but misses
claude-haiku-*.

Fix

Add a mapping for claude-haiku-4-5* / claude-haiku-4.5* → claude-haiku-4.5 in translateModelName.