fix(views): chart gradient ids survive any caller text; dashboard tables read cleanly - #2333

🟢 Confidence 10/10 · safe to merge. Contained view-layer change: every gradient and its fill come from one builder, and the new formats are pinned by rendered-scene and string tests.
_{1 note · tests covered · risk medium}

Routes every chart gradient id through a branded sanitizer, so a span name like GET (unmatched) no longer throws in the canvas painter, and formats unitless table cells instead of printing raw floats. Both behaviors are tested; one list-cell path is left unformatted.

• gradientId keeps only [A-Za-z0-9_-] and appends a hash when it rewrites
• verticalGradient now takes a branded GradientId
• formatCell trims and groups unitless numbers via plainNumber
• Lab gains a GET (unmatched) endpoint and a derived series

Before merge

• Manual · Re-add preview:web once a slot frees, to see the prod sparkline id render on a preview

Findings

Map array items through `formatCell(item, unit)` in `listCellText` (keeping the empty-string case) so list cells format like table cells.

_{782c502 · Reply "won't fix" to dismiss a finding, or mention @maple-review-bot to ask about one.}