feat(website): brand layer — teal palette, table logo, wordmark, footer

Anchor the site to the product's identity (Phase B branding):
- Accent palette mapped to the app's in-TUI teal (--sl-color-accent-*,
  light + dark); trim the splash hero's oversized desktop bottom padding.
- Header logo: a database-table glyph with a teal primary-key cell
  (light/dark variants); favicon redrawn to match.
- Landing wordmark 'RELational PLAYground': teal picks out REL+PLAY
  ('relplay', the domain) and R/D/B/M/S (spelling out RDBMS). Sizes
  locked in em off one master scale so the lockup zooms as a rigid unit.
- Footer override: default footer + an understated company (Lazy
  Evaluation Ltd) and source/issues line.

No engine names or 'DSL' in user-facing copy.

website/astro.config.mjs

@@ -25,9 +25,20 @@ export default defineConfig({
 		starlight({
 			title: 'RDBMS Playground',
 			tagline: 'Learn relational databases by doing.',
-			// TODO(Phase B): point at the real repository once it moves to its
-			// public home. Omitted for now rather than linking the wrong repo.
-			// social: [{ icon: 'github', label: 'GitHub', href: '…' }],
+			// Header logo: a database-table glyph with a teal primary-key cell.
+			// Separate light/dark files so the outline adapts to the theme;
+			// `replacesTitle: false` keeps the "RDBMS Playground" wordmark beside it.
+			logo: {
+				light: './src/assets/relplay-logo-light.svg',
+				dark: './src/assets/relplay-logo-dark.svg',
+				replacesTitle: false,
+			},
+			// Footer override: Starlight's default footer + a small company/source line.
+			components: {
+				Footer: './src/components/Footer.astro',
+			},
+			// TODO(Phase B): a header social link to the repo is deliberately omitted
+			// — the source/issues link lives understated in the footer instead.
 			customCss: ['./src/styles/global.css'],
 			// Register the simple-mode command grammar with Expressive Code (Shiki).
 			expressiveCode: { shiki: { langs: [rdbmsLang, rdbmsSyntax] } },