fix: resolve Kiro provider model mapping typo and region fallback

[alaa-alghazouli]

Description

This PR addresses two critical authorization and configuration issues within the Kiro provider:

1. Model Mapping Resolution Bug: Fixed a logical typo in claude-kiro.js where finalModel incorrectly evaluated to the original model name instead of the mapped value. This ensures models like claude-haiku-4-5 are correctly transformed to claude-haiku-4.5 before being sent to Amazon Q, preventing 403 authorization rejections.

2. Regional Configuration Fallback: Fixed an issue where the region would incorrectly fallback to us-east-1 and ignore the user's idcRegion. When users authenticate via AWS Builder ID in regions like eu-central-1, the standard region key may be omitted in favor of idcRegion. This update ensures the token's region is respected, and patches kiro-oauth.js to populate the standard region field moving forward.

Changes Made

• src/providers/claude/claude-kiro.js: Fixed MODEL_MAPPING typo in generateContent and generateContentStream. Implemented idcRegion fallback for this.region. Added missing claude-haiku-4-5-20251001 alias.
• src/auth/kiro-oauth.js: Added the region field to the saved credentials when using AWS Builder ID tokens.

These fixes resolve recurring 403 Forbidden API errors and ensure smooth multi-region deployments.