feat(settings): menu and body-text font size, and a bolder menu by default

The sidebar read as muted 13px; the menu items now use their own size at
medium weight so they carry at a glance (Todoist-ish). Both sizes are
choices under Settings → Appearance:

- Menu font size drives a dedicated --menu-size the sidebar uses.
- Body text size re-scales the shared type tokens (the list and the notes),
  the same mechanism a look uses.

The two are independent on purpose — one is a glance down a list of names,
the other a paragraph you read. Kept in localStorage like theme and look,
and applied in app.html before first paint so a chosen size does not flash
in and resize. Four steps each (Small/Default/Large/Largest); Default
carries no attribute so the base tokens stand.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

web/src/lib/components/Sidebar.svelte

@@ -1441,7 +1441,10 @@
 		border-radius: var(--radius);
 		color: var(--ink-muted);
 		text-decoration: none;
-		font-size: var(--text-sm);
+		/* Its own size (Settings → Appearance) and medium weight, so the menu items
+		   carry more than the muted small text they used to and read at a glance. */
+		font-size: var(--menu-size);
+		font-weight: 500;
 		transition:
 			background var(--fast) var(--ease),
 			color var(--fast) var(--ease);
@@ -1455,7 +1458,7 @@
 	a.active {
 		background: var(--surface-raised);
 		color: var(--ink);
-		font-weight: 500;
+		font-weight: 600;
 	}
 
 	/* Only your own projects reorder. A shared one sits where its owner put it —