- Generate lan-client/precons.js from precon-decks/precon-index.json so
PRECON_DATA is always available for local/offline mode (163 precons)
- Add scripts/generate-precons-js.js for regeneration when precons update
- Fix _loadBackendPrecons() to re-render the precon tab UI when backend
precons load successfully (was only updating status indicator text,
not populating the dropdown)
Without precons.js, PRECON_DATA was undefined and the dropdown showed
'No precon data loaded' even though 163 .dck files exist in the repo.