fix(features): label technical features as polygon (not yfinance)

[cipher813]

Summary

The Feature Catalog page on the dashboard was showing 32 technical features as source="yfinance" — the pre-T+1 label. Per the 2026-04-24 polygon migration (PRs #90/#91 split EOD/morning by source), the morning enrichment overwrites the prior-day yfinance close with polygon grouped-daily (+ VWAP) at ~5:30 AM PT every weekday. Polygon is the stable canonical source for daily OHLCV-derived features; yfinance is the same-day EOD fallback.

What changed

Flips 32 technical entries (original 26 + 6 v3.1 additions) source="yfinance" → source="polygon".

Also widens the FeatureEntry.source docstring comment to include polygon.

What's intentionally unchanged

• Macro features (vix_level, yield_10y, yield_curve_slope, gold_mom_5d, oil_mom_5d, vix_term_slope) — daily_closes.py:61 notes both yfinance (^VIX, ^TNX) and FRED (VIXCLS, DGS10) publish these. The macro collector uses FRED as canonical with yfinance for index ETFs (GLD, USO). Worth a follow-up labeling pass to split FRED-canonical vs ETF-yfinance.
• Alternative options features (put_call_ratio, iv_rank, iv_vs_rv) — yfinance is correct (polygon free tier doesn't expose options chains).

Downstream effect

The dashboard /Feature_Store page reads features/registry.json from S3, which is regenerated weekly by upload_registry(). Once the next weekly run lands, the catalog will show the corrected labels — no dashboard change needed.

Test plan

• Registry parses and generate_registry_json() still produces valid JSON
• Next weekly run uploads the updated registry; Feature Store catalog displays "polygon" for technical features

[cipher813]

Closing without merging. Per Decision 11 (source from runtime measurement, not static intent labels): the source field in registry.py is conceptually wrong as a per-feature static descriptor — it can drift from runtime ingestion reality (e.g., when polygon 403's and yfinance fills as fallback, the static label still says polygon but the data is yfinance).

Replacing-the-stale-label-with-another-stale-label doesn't fix the underlying issue. The right move is upstream-side: drop the static source column from the dashboard's catalog rendering and add a runtime-attribution panel that reads data_manifest/*.json (already carries per-source ingestion counts) for the latest-snapshot truth. That work lives in alpha-engine-dashboard, not here.

Branch fix/feature-registry-polygon-source stays around if we ever decide to keep source as an explicit "canonical/expected source" label alongside runtime attribution.