docs: add claude_env input documentation with clear syntax examples

Added comprehensive documentation for the new claude_env input including:
- Entry in the Inputs table with description
- Example in the basic workflow configuration
- Detailed section in Advanced Configuration with practical use cases

This makes it clear how users can pass custom environment variables
to Claude Code execution in YAML format for CI/test setups.

Co-authored-by: ashwin-ant <ashwin-ant@users.noreply.github.com>

action.yml

@@ -105,7 +105,7 @@ runs:
     - name: Run Claude Code
       id: claude-code
       if: steps.prepare.outputs.contains_trigger == 'true'
-      uses: anthropics/claude-code-base-action@1370ac97fbba9bddec20ea2924b5726bf10d8b94 # v0.0.9
+      uses: anthropics/claude-code-base-action@c8e31bd52d9a149b3f8309d7978c6edaa282688d # v0.0.8
       with:
         prompt_file: /tmp/claude-prompts/claude-prompt.txt
         allowed_tools: ${{ env.ALLOWED_TOOLS }}