feat: extend theme builder with block visibility, layout, effects, media, and custom CSS tabs

- Add theme-blocks.ts registry with 24 themeable blocks across 4 categories
- Extend resolver to resolve blocks, layout, effects, media, and custom CSS per scope
- Add data-theme-block attributes to all site layout blocks
- Extend ScopedThemeVars to generate CSS for block visibility, layout vars, effect vars, media vars, and custom CSS
- Rewrite admin UI with 6 tabs: Colors, Blocks, Layout, Effects, Media, Custom
- Extend server actions to save/load all new setting types
- No database migration needed - uses existing theme_scope_values table with prefixed keys

src/app/(site)/layout.tsx

@@ -22,20 +22,35 @@ export default async function SiteLayout({
 		<>
 			{session?.user?.id ? (
 				<>
-					<TopHeader session={session} />
-					<SiteHeader />
-					<Navigation session={session} />
+					<div data-theme-block="top_header">
+						<TopHeader session={session} />
+					</div>
+					<div data-theme-block="site_header">
+						<SiteHeader />
+					</div>
+					<div data-theme-block="navigation">
+						<Navigation session={session} />
+					</div>
 				</>
 			) : null}
 			<main>
-				<div className="mx-auto mt-4 grid max-w-7xl grid-cols-12 gap-x-3 gap-y-5 px-3 py-3 sm:px-4 sm:py-4 md:mt-0 md:px-6 md:py-6 md:gap-y-6">
+				<div
+					data-theme-block="content_grid"
+					className="mx-auto mt-4 grid max-w-7xl grid-cols-12 gap-x-3 gap-y-5 px-3 py-3 sm:px-4 sm:py-4 md:mt-0 md:px-6 md:py-6 md:gap-y-6"
+				>
 					<div className="col-span-12 min-w-0">
-						<MotionPageWrapper>{children}</MotionPageWrapper>
+						<div data-theme-block="page_transition">
+							<MotionPageWrapper>{children}</MotionPageWrapper>
+						</div>
 					</div>
 				</div>
 			</main>
-			<SiteFooter />
-			<RadioPlayerGate />
+			<div data-theme-block="footer">
+				<SiteFooter />
+			</div>
+			<div data-theme-block="radio_player">
+				<RadioPlayerGate />
+			</div>
 		</>
 	);
 }