[codex] Remove missing markercluster sourcemap reference

[karilint]

Summary

• Remove the sourcemap directive from the vendored leaflet.markercluster.js build.
• Keep the markercluster runtime code unchanged.

Root Cause / Context

The vendored minified markercluster file referenced leaflet.markercluster.js.map. That map exists, but it points to original ../src/*.js source files that are not included in the repository, so the frontend dev container/Vite reports missing source files during startup.

Validation

• Confirmed sourceMappingURL=leaflet.markercluster.js.map is no longer present under frontend/src/components/Map.
• npm run lint:frontend
• npm run tsc:frontend
• Commit hook also ran root npm run lint and root npm run tsc successfully.

Closes #1193