docs(market-research): add numeric-sources rubric

plugins/market-research/skills/market-research/references/numeric-sources.md

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+# Numeric Market-Data Sources (free, no API key)
+
+Phase 2 uses this to turn "search the web" into "pull THESE numbers from THESE
+places, and cite each." Prefer a real number with a source link over a vibe.
+Every number that lands in the report carries the URL it came from.
+
+## Sources & what to pull
+
+| Source | Pull | How (free) |
+|---|---|---|
+| **Google Trends** | interest-over-time, % momentum, breakout/rising queries | `trends.py "<term>"`; on `{"ok":false}` fall back to WebSearch `google trends <term>`. |
+| **play.google.com** | ranked Android packages, per-app installs/rating | `fetch-play-charts.py` for top/category charts; `play.py resolve` for per-app installs/rating. |
+| **Sensor Tower (blog/reports)** | downloads, revenue, DAU, YoY growth | WebSearch `sensortower <category> revenue downloads 2026`; WebFetch the article; quote the figure + date. |
+| **data.ai / Apptopia posts** | top-charts movement, market revenue | WebSearch `data.ai <category> market 2026`; WebFetch + cite. |
+| **Statista (free public charts)** | market size $, user counts, CAGR | WebSearch `statista <category> market size`; use the visible free figure only; cite. |
+| **SimilarWeb (free tier)** | incumbent web traffic, engagement | WebSearch `similarweb <incumbent domain>`; cite visits/engagement. |
+
+## Query shaping (vary by the run's angles)
+
+- Always bind a year: `... 2026` so figures are current.
+- Bind a region when the angle is regional: `... <category> Brazil downloads`.
+- For growth: `fastest growing <category> apps 2026`, `<category> market size 2026`.
+- For incumbent weakness: `<incumbent> complaints reddit`, `<incumbent> alternative 2026`.
+
+## Citation rule
+
+Each extracted number is written as `<number> [<source>](<url>)` in the report.
+A claim with no source link is downgraded to a qualitative note, not a number —
+it must NOT be used to justify a numeric subscore (see scoring-guide.md).
+
+## When a source is paywalled / JS-only
+
+Do not scrape it. Use the figure only if it's visible free (article body, public
+chart). Otherwise drop to the next source. Never invent a number to fill a gap.