Close open questions in server design doc

- No grid in web view (writing aid only)
- No per-page share links for now (URL structure supports it later)
- No server-side deletion — server mirrors tablet exactly via sync

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/SERVER_DESIGN.md

@@ -406,15 +406,16 @@ rp_origins      = ["https://pad.metacircular.net"]
 level = "info"
 ```
 
-## Open Questions
+## Design Decisions
 
-1. Should the web UI show the grid? It's excluded from PDF/JPG export
-   but might be useful for on-screen viewing. Could be a toggle.
+1. **No grid in web view.** The grid is a writing aid on the tablet
+   only. SVG, JPG, and PDF renders are all gridless.
 
-2. Should share links support per-page scope in addition to whole
-   notebook? The user said no for now, but the URL structure supports
-   it (`/s/:token/pages/:num`).
+2. **No per-page share links for now.** The URL structure supports
+   per-page access (`/s/:token/pages/:num`), so adding it later is
+   trivial. For now, shared links always scope to the whole notebook.
 
-3. Should the server support deleting individual pages, or only
-   full notebook replacement via sync? Full replacement is simpler
-   and matches the "server receives whatever the app pushes" model.
+3. **No server-side page deletion.** The server is a mirror of the
+   tablet. `SyncNotebook` replaces all data for a notebook — if a
+   page was deleted on the tablet, it disappears from the server on
+   the next sync. The server never modifies notebook content.