Add snippet metadata panel, duplicate, and immediate-load preview (M4.5)

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

@@ -472,6 +472,14 @@ reset: () => set({ snippets: [], activeSnippetId: null, draftSpec: '' });
 - Do persistence and external sync (IndexedDB, `localStorage`, URL hash, theme) in
   startup `subscribe` listeners via `infrastructure/` adapters.
 - Debounce expensive reactions (auto-save, re-render) inside the subscriber.
+- Advance a snippet's `modified` on **every** save the library sorts by — draft
+  auto-save, inline name/comment edits, publish, revert, rename-propagation — so
+  Modified-descending keeps the just-touched snippet on top (spec §02 → Sort).
+- Bump `SnippetStore.bufferEpoch` only on a _programmatic_ buffer load (select /
+  create / duplicate / revert / hydrate) — it is the "reload the editor, this isn't
+  a keystroke" signal consumed by both the Monaco buffer and the preview's
+  immediate-render path (arch 05 §5). Metadata edits (name/comment) advance
+  `modified` but must **not** bump it — they aren't in the spec buffer.
 - Import singleton store hooks directly in the leaves that need shared state.
 
 **Don't**