feat: F&G column, the stock's fear-and-greed reading on every report row

[yanivil]

Description

Puts the per-ticker fear-and-greed reading of #112 on the report as information, the way the market context was added in #105. No rule uses it.

• scan.fear_greed (with Wilder's RSI in scan._rsi): the composite moves from tools/backtest.py into the scanner so the report and the replay share one implementation; the backtest imports it. Constants FG_RSI_LEN, FG_BB_LEN, FG_MACD, FG_LOOKBACK join the constants block with the replay evidence in the comment.
• Signal.fear_greed: one reading per symbol at the last close, set by scan_symbol on every row of that symbol; fear_greed in signals.json.
• Report: a 14th column F&G after Vol×, and a footer sentence: above 80 the stock is stretched and such breakouts replayed worst, below 20 it is washed out, information only.
• Wiki 01 output contract, wiki 03 pointer from the tested section to the column, README sample-output paragraph, changelog.
• The Claude desktop e-mail task's prompt now knows the column and takes the column list from each table's own header row, so it works on reports with or without F&G regardless of when this merges.

Real-data run on 10 tickers: HAL's confirmed breakout reads 73.9, the PH and HAS cup bases read 20.3 and 17.2.

Verified: ruff clean, 137 tests pass (the composite tests moved to scan, scan_symbol sets one reading per symbol and a bare detector does not, the report's 14 columns with the F&G cell equal to the symbol's composite, the footer sentence, and the replay row's fear_greed equal to its fg_score feature).

Related Issues

Related: #113 (the stretch gate), #112 (the features), #101 and #99 (context)

Checklist

• Code follows existing project style and type annotations
• Threshold changes include a one-line "why" comment in scan.py (four new constants, commented; no threshold changed)
• Offline unit tests pass (python -m pytest -q)
• Random-walk false-positive rate stays under 5% (detection logic untouched)
• Documentation updated in docs/wiki/
• CHANGELOG.md updated

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