Implements load_and_prepare_data (JSONL ingestion with class filtering),
compute_class_weights (inverse-frequency, div-by-zero safe), compute_metrics_for_trainer
(macro F1 + accuracy), and WeightedTrainer.compute_loss (**kwargs-safe for
Transformers 4.38+ num_items_in_batch). All 12 tests pass.
Two bugs fixed:
1. Blank white page after vue SPA rebuild: browsers cached old index.html
referencing old asset hashes. Assets are deleted on rebuild, causing
404s for JS/CSS -> blank page. Fix: serve index.html with
Cache-Control: no-cache so browsers always fetch fresh HTML.
Hashed assets (/assets/chunk-abc123.js) remain cacheable forever.
2. Queue draining to empty on skip/discard: handleSkip and handleDiscard
never refilled the local queue buffer. After enough skips, store.current
went null and the empty state showed (blank-looking). Fix: both handlers
now call fetchBatch() when queue drops below 3, matching handleLabel.
Also: sync classifier_adapters LABELS to match current 10-label schema
(new_lead + hired, remove unrelated).
48 Python tests pass, 48 frontend tests pass.
