Reporting flags: --report extension detection misses .markdown/.htm, --baseline silently ignored without --report

[mcclowes]

Found during a docs accuracy audit. Two related rough edges in src/cli/handlers/compile.ts:

1. Report format detection (compile.ts:227-231) only special-cases .html and .md — report.markdown or report.htm silently gets JSON content with a misleading extension. Consider recognising both aliases, or warning when the extension is unrecognised.

2. --baseline is only read when --report is set (compile.ts:199-224). With --audit-log alone it is parsed and silently discarded. Consider erroring or warning when --baseline is passed without --report.

Docs (CLAUDE.md, README, docusaurus CLI page) have been updated to state the current behavior.