Fix remaining QA issues: technicals, caches, engine, screener

[mikejamescalvert]

Summary

Addresses the remaining issues from the comprehensive QA audit (PR #115 covered the first 10).

Technical Analysis (6 fixes)

• daily_return_pct crash — IndexError when <2 bars. Now guarded.
• Weekly trend proxy broken — Was sampling every 5th bar from the ENTIRE dataset instead of the last 60 bars. Fixed to close.iloc[-60:].iloc[::5].
• NaN values leak downstream — All indicator outputs now filtered through math.isnan check. Prevents AI from seeing NaN in analysis.
• Missing momentum indicators — Added ADX (trend strength) and ROC (rate of change). Critical for momentum confirmation that was missing.
• BB width not normalized — Added bb_width_pct for cross-symbol volatility comparison.
• Generic Exception catch — Replaced with specific types + logging for debuggability.

Data Provider Cache Fixes (4 fixes)

• Timezone bugs in ALL cache loaders — datetime.fromisoformat() could return naive datetimes. Comparing with datetime.now(tz=UTC) would raise TypeError. Fixed in fundamentals, earnings, and crypto_market.
• Earnings HTTP error unhandled — urlopen() had no try/except around it. Now catches and logs HTTP errors.
• Past earnings returned from live fetch — Cache loader filtered days_until < 0 but live fetch didn't. Fixed.

Strategy Engine (2 fixes)

• Zero-price buy orders — If current_price was 0 (corrupted data), would divide by zero or create invalid orders. Now validates > 0 before using.
• Zero-price sell limit orders — Limit price of $0.00 from corrupted position data. Now skips limit order generation when price is 0.

Broker (1 fix)

• Crypto detection too broad — endswith("USD") would misidentify stock tickers as crypto (applying wrong time-in-force). Removed; now uses only asset_class enum and / in symbol.

Screener (2 improvements)

• VIX-adaptive thresholds — Screening thresholds now adjust to market volatility: stricter in low-vol (VIX < 15), relaxed in high-vol (VIX > 25).
• Auto-add top picks to watchlist — Top 3 screener candidates now auto-added to TRADING_WATCHLIST for immediate trading. Previously, screener only created a GitHub issue and candidates waited days for the weekly watchlist review.

Test plan

• All 270 tests pass
• Ruff lint clean
• mypy strict clean (38 source files)
• Verify ADX/ROC appear in trading agent analysis logs
• Verify screener auto-adds to watchlist on next run
• Verify cache timezone fix prevents TypeError on next cycle

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