Add 32 factor-combo strategies with configurable rebalancing frequency

New FactorComboStrategy class (strategies/factor_combo.py) implements
8 champion factor signals (4 US, 4 CN) discovered through iterative
factor research, each at 4 rebalancing frequencies (daily/weekly/
biweekly/monthly). Registered in trader.py as fc_{signal}_{freq}.

Existing strategies and state files are untouched — safe to git pull
and restart monitor on server.

Also includes factor research scripts (factor_loop.py, factor_research.py,
etc.) used to discover and validate these factors.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitignore

@@ -21,6 +21,14 @@ data/universe_*.json
 # Trader state — per-machine, regenerated by auto/simulate
 data/trader_*.json
 
+# Factor attribution output and cached factors
+data/attribution_*/
+data/factors/
+data/factors_review_tmp/
+
+# External tool artifacts
+docs/superpowers/
+
 # IDE / editor
 .idea/
 .vscode/