Fix: market classifier never classified any market

[mpont91]

The job that populates aware_market_classifications looks for pending markets with:

LEFT JOIN polybot.aware_market_classifications c FINAL
    ON t.market_slug = c.market_slug
WHERE t.market_slug != ""
  AND c.market_slug IS NULL

In ClickHouse an unmatched LEFT JOIN row yields the column type's default rather than NULL unless join_use_nulls is set. market_slug is LowCardinality(String), so an unclassified market comes back as the empty string and IS NULL never matches. get_unclassified_markets() returns an empty list on every run and the job logs "No markets to classify".

The same predicate appears in get_stats(), which therefore always reports zero unclassified markets.

Effect

aware_market_classifications stays empty forever. Because the category views join through it, that leaves:

• market_category blank on every row of aware_global_trades
• aware_trader_category_distribution returning an empty category for every trader
• aware_category_stats reporting everything as UNCLASSIFIED
• the sectorial PSI indices (PSI-CRYPTO, PSI-POLITICS, PSI-SPORTS) with no eligible members, since they filter by category

Fix

Compare against the empty string instead.

Verified

Against a database with 8,243 distinct traded markets:

before: SELECT count() ... AND c.market_slug IS NULL  ->     0
after:  SELECT count() ... AND c.market_slug = ""     ->  8243

A run of the fixed job classified all 8,243:

CRYPTO 1677 | POLITICS 640 | SPORTS 263 | ENTERTAINMENT 71
ECONOMICS 50 | SCIENCE 48 | NEWS 21 | OTHER 5473

and aware_trader_category_distribution now returns real categories (5,003 traders with CRYPTO exposure, 665 POLITICS, 318 SPORTS).