Dashboard static files 404 unless the server runs from the repo root

## Context

`handleStaticFile` resolves the static root as the relative path `visualization/static`, so it depends entirely on the process working directory. Running `./pinnaclemm --enable-visualization` from `build/` (the documented way) makes every static request 404, including `/index.html`. That is why the docs tell users to open the dashboard HTML straight from the filesystem instead of from the server.

## What to do

- Resolve the static directory relative to the executable location, with a `--static-dir` flag to override it.
- Fall back to the current relative path if neither resolves, and log the directory actually being served at startup.
- Update the README and visualization docs so the dashboard is opened from `http://localhost:/` once this works.

## Notes

Keep this coordinated with the path traversal fix in #76 since both touch the same function.

Start by inspecting handleStaticFile and the documented ./pinnaclemm --enable-visualization invocation from build/. Verify that /index.html is served at the localhost API port, that --static-dir and the fallback behave as specified, and that startup logs the served directory; then update the README and visualization documentation. Coordinate changes with path traversal fix #76, which touches the same function.

Written by the indexing model from the issue text.