Add tools/undervalued.py: trading strategy, goods priced below production cost

Finds manufactured goods currently selling below their implied
production cost (live input cost vs output price) - candidates to buy
and hold for a price-reversion bounce, the mirror of the "is this
worth building" question saturation.py already answers.

Backtested first (326 output tickers, 287 deduplicated dip-onset
episodes across 112 distinct tickers): +3mo forward return mean
+21.3%/median +8.9%/73.2% hit rate at >=10 units/day volume - real
signal, not noise, but only ~0.10-0.24%/day, far below the 14-29%/day
marginal ROI this session's production builds found. Documented
prominently in the tool's own docstring and CLAUDE.md so it doesn't
get mistaken for a primary strategy - it's for excess idle capital
once better-yielding builds are exhausted, not before.

Promoted daily_prices() out of tools/history.py into puga/history.py
so both tools share it, per the self-improve rule.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tools/history.py

@@ -4,18 +4,11 @@ Daily price = value traded / units traded (VWAP), forward-filled over days witho
   tools/history.py KV                       # AI1, the recipe producing KV
   tools/history.py BHP --cx AI1 --eff 1.18 --overhead 3200 --capex 94000 --months 12
 Building/day = batches/day at --eff; profit/day = batches/day * margin_per_batch - overhead (wages etc, --overhead)."""
-import argparse, datetime, statistics, sys
+import argparse, statistics, sys
 from pathlib import Path
 sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
 from puga import config, fio
-
-
-def daily_prices(tk, cx):
-    out = {}
-    for e in fio.cxpc(tk, cx):
-        if e.get("Interval") == "DAY_ONE" and e.get("Traded"):
-            out[datetime.datetime.fromtimestamp(e["DateEpochMs"] / 1000, datetime.timezone.utc).date()] = (e["Volume"] / e["Traded"], e["Traded"])
-    return out
+from puga.history import daily_prices
 
 
 def main():