Per-chart export: copy/download spec and PNG/SVG from the preview header

docs/architecture/01-state-and-stores.md

@@ -194,10 +194,13 @@ ephemeral request state, not durable data:
 
 - **`useConfirmStore`** — the blocking confirm dialog (the `window.confirm` replacement).
 - **`useNotificationStore`** — non-blocking toasts (failed saves, etc.).
-- **`useSettingsPopoverStore`** — which per-pane settings disclosure is open (one
-  at a time); its imperative `openSettingsPopover(id)` lets the Cmd/Ctrl+, shortcut
-  open the editor cluster. The disclosure widget contract (gear + non-modal popover,
-  not an ARIA menu; Esc/focus rules) is [10 · Interaction & Feedback](10-interaction-and-feedback.md) §5.
+- **`useSettingsPopoverStore`** — the single-open registry for **all** pane-header
+  disclosures (the per-pane settings clusters and the per-chart Export control), keyed
+  by id so at most one is open at once; its imperative `openSettingsPopover(id)` lets the
+  Cmd/Ctrl+, shortcut open the editor cluster. Header disclosures share this registry rather
+  than each carrying their own open-state. The disclosure widget contract (trigger +
+  non-modal popover, not an ARIA menu; Esc/focus rules) is
+  [10 · Interaction & Feedback](10-interaction-and-feedback.md) §5.
 
 Each pairs its store with a thin **imperative trigger** exported alongside the hook —
 `confirm(opts): Promise<boolean>` and `notify(opts): string` — so orchestration/services can