docs: keep real data; drop synthetic suggestion; disclose Yahoo personal-use terms

Per the owner decision to use real (not synthetic) data: the sample-data README
no longer offers a 'deterministic synthetic fixture' as an alternative for the
committed showcase data. It now states plainly that the snapshot is real market
data and discloses that yfinance documents Yahoo Finance data as intended for
personal use, pointing the reader to observe Yahoo's terms (kept as an
owner/legal decision - not characterized as negligible). The real-data
local-regeneration and --live paths are retained.

No data migration: a cleanly-redistributable real source for this ETF universe
is not reachable here (Stooq is anti-bot blocked; FRED's equity indices carry
third-party copyright and it covers only public-domain macro series), so the
real Yahoo-sourced snapshot is kept and honestly documented.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: magnaprog

quantcortex/data/sample/README.md

@@ -11,14 +11,16 @@ this file reproduces the numbers bit for bit. Without a fixed snapshot the
 results would drift: `yfinance` re-adjusts historical closes over time as
 dividends accrue, so every live fetch returns slightly different data.
 
-**Provenance / licensing.** Derived from Yahoo Finance via `yfinance` for
-reproducible examples and tests only. Whether committing this Yahoo-derived
-snapshot is acceptable for a given use (private repo, redistribution, etc.) is a
-repo-owner / legal decision this file cannot settle; if in doubt, the safest
-alternatives are a deterministic synthetic fixture, or keeping real data
-local-only by passing `--live` to `scripts/generate_report.py` (which fetches
-fresh and writes nothing). It is not an authoritative or survivorship-safe
-source. Regenerate or extend the committed snapshot with:
+**Provenance / licensing.** This is *real* market data (not synthetic), derived
+from Yahoo Finance via `yfinance` for reproducible examples and tests. Note that
+`yfinance` documents Yahoo Finance data as intended for **personal use**;
+whether committing this Yahoo-derived snapshot to a given repo (public,
+redistributed, or commercial) is acceptable is a repo-owner / legal decision
+this file cannot settle, so observe Yahoo's terms for your use. To avoid relying
+on the committed copy, regenerate it locally (below) or pass `--live` to
+`scripts/generate_report.py`, which fetches fresh and writes nothing. It is not
+an authoritative or survivorship-safe source. Regenerate or extend the committed
+snapshot with:
 
 ```bash
 python -c "from quantcortex.data.providers.yfinance_provider import YFinanceProvider; \