[CLI] Expose new Core features via flags

[jeffpatton1971]

Summary
Add flags: --anchor-algorithm, --template, --front-matter, --auto-link, --alias-map, --external-docs, --toc, --namespace-index, --parallel, --diff, --dry-run, --report. Map Core diagnostics to console; non-zero exit on errors only.

Tasks

• Wire options to RendererOptions and core services.
• ConsoleDiagnosticSink implementation.
• Wrap with RendererRunner for diff/dry-run/report.

Acceptance

• Defaults preserve 1.3.1 behavior.
• Smoke tests for --diff, --dry-run, --report.