[P3] Report: prune dangling `ReportColumnSchema`/`ReportGroupingSchema` exports + retire the legacy `ReportViewer` fallback

[os-zhuang]

Deep-cleanup follow-up from the report-chart disposition (#3441, umbrella #1878). #3441 was the non-breaking accuracy fix; these two items are breaking / cross-repo and were deferred.

1. Prune the dangling ReportColumnSchema / ReportGroupingSchema

After the ADR-0021 single-form cutover, a dataset-bound report expresses columns/grouping as dataset measure/dimension name arrays (rows/columns/values = z.array(z.string())). ReportColumnSchema / ReportGroupingSchema (packages/spec/src/ui/report.zod.ts:26-41) are referenced by no schema body — they survive only as public type exports (ReportColumn/ReportGrouping/…Input) and were marked @deprecated in #3441.

• Remove the schemas + their type exports from @objectstack/spec.
• Remove the objectui re-exports (@object-ui/types spec-report.ts SpecReportColumn* / SpecReportGrouping*, index.ts:694-712).
• Breaking (public exports) → schedule with a major + a one-line migration note. Coordinated framework + objectui PRs.

2. Retire the legacy ReportViewer chart path

DatasetReportRenderer (objectui) is the live, primary report renderer — it plots the spec chart.xAxis/yAxis as dataset dimension/measure via useDatasetRows. The older ReportViewer (reads the invented xAxisField/yAxisFields, ReportViewer.tsx:326-330) is only a fallback now (app-shell/.../ReportView.tsx:502-508).

• Evaluate whether the ReportViewer fallback still has any reachable callers; if not, retire the legacy chart branch (and the groupBy it alone consumed — marked experimental in docs(spec): correct ReportChart xAxis/yAxis semantics; mark dead report surface (#1890) #3441).

Refs #1878, #1890, #3441.

[os-zhuang]

Both deferred items shipped across two coordinated PRs.

1. Pruned the dangling ReportColumnSchema / ReportGroupingSchema ✅

• framework feat(spec)!: prune dead ReportColumnSchema/ReportGroupingSchema exports + unread report chart groupBy (#3463) #3488 — removed ReportColumnSchema / ReportGroupingSchema + their type exports (ReportColumn / ReportGrouping / …Input) from @objectstack/spec/ui, dropped the manifest keys ui/ReportColumn / ui/ReportGrouping, and regenerated content/docs/references/ui/report.mdx + the API-surface snapshot.
• objectui feat(report)!: drop SpecReportColumn/SpecReportGrouping re-exports + retire legacy ReportViewer chart fallback (#3463) objectui#2816 — removed the SpecReportColumn* / SpecReportGrouping* re-exports from @object-ui/types (spec-report.ts + index.ts) and the matching assertion in spec-ui-schema-reexports.test.ts.
• Bonus: also removed ReportChart.groupBy (the [EXPERIMENTAL — not enforced] field from docs(spec): correct ReportChart xAxis/yAxis semantics; mark dead report surface (#1890) #3441) — nothing read it after the ReportViewer retirement below. ReportChartSchema is non-strict, so residual chart.groupBy in stored metadata is silently stripped on parse; no tombstone needed.

2. Retired the legacy ReportViewer chart fallback ✅

The ReportViewer fallback branch in app-shell ReportView.tsx was confirmed unreachable by any shipped metadata: it fired only when a report had neither dataset nor objectName, the Studio inspector only ever writes the dataset-bound shape, and no seed/example authored type: 'report-viewer'. objectstack-ai/objectui#2816:

• ReportView now routes every report through the spec ReportRenderer dispatcher (dataset → DatasetReportRenderer, stored pre-9.0 JSON → presentation bridge, pre-spec { data, columns } → LegacyReportRenderer). Deleted the ReportViewer last-resort branch, the mapReportForViewer spec→legacy chart-section adapter (the sole producer of xAxisField / yAxisFields), and the now-dead data-fetch loading flag.
• plugin-report ReportViewer.tsx: removed the chart-section branch (it read the invented xAxisField / yAxisFields, never the spec's xAxis / yAxis, and was only fed by the deleted adapter).

Why ReportViewer the component was kept (not deleted outright): its table / summary / text sections still back the registered report-viewer component and the pre-9.0 specReportToPresentation bridge in ReportRenderer. Only the dead chart branch and the fallback routing were retired.

Shipped as minor

Per the launch-window breaking-as-minor policy (precedent: remove-enable-trash-mru) — the major guard would otherwise block the PR. Both changesets carry the FROM→TO migration.

Verification

Browser-dogfooded against the showcase backend: the summary (Hours by Status), matrix (Status × Priority, with server totals) and joined (Task Overview) reports all render correctly through DatasetReportRenderer after the fallback removal. Framework: 6857 spec tests + all generated-artifact / API-surface / changeset / liveness gates green. objectui: 60/60 dependent type-checks + all test shards green.

Refs #1878, #1890, #3441.