chore(spec): changeset for the chart drillDown mode guidance rewording

patch — the guidance sentence ships as source (chart.zod.ts is in
@objectstack/spec's published src/**/*.zod.ts) and as a runtime string in
dist/ui/index.{js,mjs}; no accept/reject behaviour moves.

Co-authored-by: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QcAS3qiYYZNezaxZxaUdMV

Author: claude

.changeset/20152-chart-drilldown-mode-guidance.md

@@ -0,0 +1,41 @@
+---
+'@objectstack/spec': patch
+---
+
+`ChartDrillDownSchema`'s refusal text for `drillDown.mode` names the one objectui block that reads it, not all three it used to
+
+An author (or an AI) who writes `drillDown.mode` on a chart gets this guidance
+sentence back from `objectui validate` / `safeValidateSchema`. It used to read:
+
+> `mode` (`'filter'` | `'record'`) is a TABLE / PIVOT / METRIC drill key, not a
+> chart one: …
+
+`object-metric` has refused `drillDown.mode` at its TypeScript door since
+objectui#9002 (PR objectui#10681, merged, on the maintainer ruling recorded
+there, comment `5643445104`), and `object-pivot` has refused it since
+objectui#10685 (PR objectui#10710, merged). Measured on objectui `origin/main`:
+neither block's renderer ever read `mode`; only `object-data-table` does. So
+the old sentence sent an author who followed it straight into a second
+refusal on two of the three blocks it named — right on `object-pivot` and
+`object-metric` (both now refuse the key by name), and a stored JSON config
+that carries it there is silently ignored with no diagnostic.
+
+The sentence now names the one block that actually reads `mode`:
+
+> `mode` (`'filter'` | `'record'`) is objectui's `object-data-table` drill
+> key, not a chart one: …
+
+The reasoning clause and "Delete the key" are unchanged. The neighbouring
+`report` guidance entry (a METRIC / PIVOT widget capability) is untouched —
+its blocks were not remeasured on this card.
+
+⛔ No accept/reject behaviour changes. `mode` remains refused on
+`ChartDrillDownSchema` exactly as before; only the refusal text changes.
+
+**This is shipped, which is why it carries a changeset rather than
+`skip-changeset`.** `@objectstack/spec`'s published `files[]` ships both
+`dist` and `src/**/*.zod.ts`, and `chart.zod.ts` is one of the latter — so the
+sentence ships as source verbatim, and also as a runtime string built into
+`dist/ui/index.js` / `dist/ui/index.mjs` (measured: present at 1 occurrence
+each after a rebuild, with the old "TABLE / PIVOT / METRIC" spelling absent
+from both).