feat: display syntax errors for settings and workflow config

[atharva-deopujari]

Summary

Syntax errors in .claude/settings.json and workflow inputs like allowed_tools are currently silently ignored, making debugging difficult for users. This adds clear error messages when configuration has issues.

Changes

base-action/src/setup-claude-code-settings.ts

• Surface JSON parse errors with the specific syntax error message when .claude/settings.json or the settings input contains invalid JSON
• Use core.warning() for recoverable issues (corrupt existing file) and core.error() for blocking issues (bad input)

base-action/src/parse-sdk-options.ts

• Detect YAML list markers (- prefixes) in allowed_tools / disallowed_tools entries, a common mistake when using pipe (|) notation in workflow YAML
• Emit core.warning() with a corrective example and strip the markers so tools still work

Tests

• 3 new tests for settings JSON validation
• 4 new tests for YAML marker detection

All 42 tests pass. Typecheck clean.

Fixes #242

[atharva-deopujari]

Closing - looks like this has already been addressed. Thanks!