Add brand logo, favicon, and purple accent (#8844ae)

- site/src/assets/logo.svg: waveform-"P" mark, recolored to #8844ae, cropped
  tight, transparent background; shown in the Starlight header.
- site/public/favicon.svg: matching mark, white on a purple rounded tile.
- site/src/styles/theme.css: brand accent (#8844ae) for light + dark themes.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Mikkel Bergmann

site/astro.config.mjs

@@ -21,7 +21,9 @@ export default defineConfig({
     starlight({
       title: 'Podscript',
       description: 'Podcasts as code — write your episode as one plain-text file and compile it to identical audio every time.',
+      logo: { src: './src/assets/logo.svg', alt: 'Podscript' },
       favicon: '/favicon.svg',
+      customCss: ['./src/styles/theme.css'],
       social: [{ icon: 'github', label: 'GitHub', href: GITHUB }],
       // No editLink: pages are generated from ../docs by scripts/sync-docs.mjs, so a
       // per-page edit URL would point at a gitignored file. Edit the canonical docs/ instead.

site/public/favicon.svg

@@ -0,0 +1,15 @@
+/* SPDX-FileCopyrightText: 2026 Mikkel Bergmann */
+/* SPDX-License-Identifier: MIT */
+
+/* Brand accent — Podscript purple (#8844ae). Starlight's :root is the dark theme. */
+:root {
+	--sl-color-accent-low: #341a47;
+	--sl-color-accent: #9a52c9;
+	--sl-color-accent-high: #e7cff6;
+}
+
+:root[data-theme='light'] {
+	--sl-color-accent-low: #f0e2f9;
+	--sl-color-accent: #8844ae;
+	--sl-color-accent-high: #401a58;
+}