Fix OAuth authentication by using claude_code_oauth_token parameter

- Extract access token from credentials JSON in prepare.ts
- Pass token to base action via claude_code_oauth_token parameter
- Remove unused OAuth setup code and CLAUDE_CREDENTIALS env var
- This uses the official base action's OAuth support correctly

action.yml

@@ -109,7 +109,6 @@ runs:
         GITEA_API_URL: ${{ env.GITHUB_SERVER_URL }}
         # Only set ANTHROPIC_API_KEY if not using OAuth
         ANTHROPIC_API_KEY: ${{ inputs.anthropic_api_key != 'use-oauth' && inputs.anthropic_api_key || '' }}
-        CLAUDE_CREDENTIALS: ${{ inputs.claude_credentials }}
 
     - name: Run Claude Code
       id: claude-code
@@ -125,6 +124,7 @@ runs:
         use_bedrock: ${{ inputs.use_bedrock }}
         use_vertex: ${{ inputs.use_vertex }}
         anthropic_api_key: ${{ inputs.anthropic_api_key }}
+        claude_code_oauth_token: ${{ steps.prepare.outputs.claude_oauth_token }}
       env:
         # Core configuration
         PROMPT_FILE: /tmp/claude-prompts/claude-prompt.txt
@@ -138,7 +138,6 @@ runs:
         USE_VERTEX: ${{ inputs.use_vertex }}
         # Only set ANTHROPIC_API_KEY if not using OAuth
         ANTHROPIC_API_KEY: ${{ inputs.anthropic_api_key != 'use-oauth' && inputs.anthropic_api_key || '' }}
-        CLAUDE_CREDENTIALS: ${{ inputs.claude_credentials }}
 
         # GitHub token for repository access
         GITHUB_TOKEN: ${{ steps.prepare.outputs.GITHUB_TOKEN }}