Premium Analytics: document widget conventions and Stats porting patterns

[dognose24]

Why

Code review on the Locations (#49513), Devices (#49928), and Search Terms (#49985) widget ports surfaced a set of recurring mistakes and missing patterns — attribute type locality, `presentation` source of truth, `max = 0` semantics, the two-component WidgetRoot structure, and more. This PR consolidates those into shared agent guidance so future batch ports have one source of truth instead of rediscovering them in review.

What

`.agents/rules/widgets.md`

• New Two-component structure section: outer component wraps ``, inner calls `useWidgetRootContext()`; explains why the split is required and that `reportParams` always comes from context, never from `attributes`

`projects/packages/premium-analytics/AGENTS.md`

• General Pitfalls: `@jetpack-premium-analytics/*` alias rule, English-only comments
• Widget pitfalls (5 new): `presentation` only in `widget.json`; attribute type declared once in `widget.ts` and imported; ``; no inline styles; check toolkit helpers before reimplementing
• New Stats widgets section covering: data hooks already exist in `packages/data/`; data access path (`primary.data → .data?.[0]?.items`); `max = 0` means all rows; loading/stale-data strategy; comparison placeholders; visual conventions (title variant, dataFormat, row height, emptyStateText, picker aspect ratio)

`.agents/skills/widget-audit.md`

• Shape: `widget.ts` must not declare `presentation`; ghost attribute check; `@jetpack-premium-analytics/*` alias enforcement
• Contract: attribute type `T` imported from `../widget`, not re-declared in `render.tsx`
• Chrome: `presentation` value vs actual layout consistency check
• Style + i18n: no inline styles; explicit `` type; i18n covers data-transform layer; English comments

Does this pull request change what data or activity we track or use?

No.

Testing instructions

Documentation-only change — no runtime code is modified. To verify:

• Read the three updated files and check that the conventions accurately reflect the patterns in the ported widgets (Premium Analytics: port the Locations stats widget #49513, Premium Analytics: port Stats Devices and Top Platforms widgets #49928, Premium Analytics: port Stats Search Terms widget #49985).
• Optionally run `/widget-audit ` against an existing widget (e.g. `search-terms`) to confirm the updated checklist produces sensible output.

🤖 Generated with Claude Code

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Code Coverage Summary

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