EpicsDocsOptions defaults to writing .md files into cwd

[gilesknap]

Summary

EpicsDocsOptions.output_dir defaults to Path("."), so any IOC that constructs EpicsDocsOptions() without arguments will silently drop {controller_id}.md (one per top-level controller) plus index.md into whatever directory the IOC was launched from.

For us this means launching fastcs-catio from a repo root creates an untracked BL12I-EA-RIO-01.md in the working tree on every start.

Where

• src/fastcs/transports/epics/options.py:13 — output_dir: Path = Path(".")
• src/fastcs/transports/epics/emission.py:116 emit_docs_files() — path = output_dir / f"{name}{DOCS_EXT}" then path.write_text(...), called from both CA (ca/transport.py:49) and PVA (pva/transport.py:46) transports whenever self.docs is set.

The sibling EpicsGUIOptions has the same Path(".") default but is almost always overridden by callers (we do, in fastcs_catio/__main__.py). The docs option tends to be left at its default because the typical use is just EpicsDocsOptions().

Tested against fastcs 0.14.0.

Suggested fix

A few options, in rough order of preference:

1. Drop the default entirely and make output_dir required, so callers must opt into a location.
2. Default to something less surprising than cwd — e.g. a docs-gen/ subdir, or None meaning "don't emit". Same treatment would make sense for EpicsGUIOptions.output_dir.
3. At minimum, document the cwd default prominently on the dataclass so users know to set it.

Happy to send a PR if you have a preference.