Harden weather engine for Polymarket trading

[jestkent]

Correctness:

• Fix freezing-point temp bug (0.0C stored as 0F instead of 32F)
• Dedup observations: migration + UNIQUE(station_id,timestamp) + INSERT OR IGNORE
• Fix cli_final KeyError on stations missing cli_code; add all 10 cli_codes
• Use local-day (not UTC) boundary for daily high/low in pace_model

Speed:

• app.py: cache static gridpoint resolve + short-TTL forecast/DB reads (forecast now 1 API call/rerun instead of 3), reuse requests.Session

Features:

• Add weather/signal.py: projected daily high vs market threshold lean
• Wire cli_final into run_forever scheduler (~hourly)

Reliability/docs:

• UTF-8 console guard so scripts stop crashing on Windows cp1252
• Add CLAUDE.md and pinned requirements.txt