Add distributed settings and workspace import/export (M5)

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

@@ -179,8 +179,13 @@ Each cohesive feature owns a store holding its durable domain state.
 - **`useSnippetStore`** — the snippet library: `snippets`, `activeSnippetId`, the
   working `draftSpec`, and its actions.
 - **`useDatasetStore`** — loaded datasets, the active dataset, inferred fields.
-- **`useSettingsStore`** — user preferences (editor options, render debounce,
-  date format, theme); mirrors what gets persisted to `localStorage`.
+- **`useUserSettingsStore`** — the **managed** user preferences applied _live_ as
+  `saved` (editor options, render debounce, date format). Its per-cluster setters
+  are called by the per-pane settings popovers; the editor/preview/library read
+  `saved.*`. There is **no draft/Apply** — settings are distributed and commit on
+  change (spec §07). **UI theme and preview fit mode are NOT here** — they're
+  cross-cutting and live in `useAppStore` (header toggle, Fit control); all three
+  persist to the one `astrolabe:settings` record via slice writers (arch 02 §5).
 
 ### Global overlay stores (imperative trigger)
 
@@ -189,6 +194,10 @@ 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.
 
 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