docs: add VitePress documentation site with GitHub Pages deployment

Rewrites all documentation with accurate project details (Fastify, port
1349, single-container Docker, all 33+ tools, full database schema).
Adds getting started guide and configuration reference. Updates help and
settings dialogs to link to the docs site.

apps/docs/.vitepress/config.mts

@@ -0,0 +1,59 @@
+import { defineConfig } from 'vitepress'
+
+export default defineConfig({
+  title: "Stirling Image",
+  description: "Documentation for Stirling Image, a self-hosted image processing suite.",
+  base: '/Stirling-Image/',
+  srcDir: '.',
+  outDir: './.vitepress/dist',
+
+  head: [
+    ['meta', { name: 'theme-color', content: '#3b82f6' }],
+  ],
+
+  themeConfig: {
+    nav: [
+      { text: 'Home', link: '/' },
+      { text: 'Guide', link: '/guide/getting-started' },
+      { text: 'API Reference', link: '/api/rest' }
+    ],
+
+    sidebar: [
+      {
+        text: 'Guide',
+        items: [
+          { text: 'Getting started', link: '/guide/getting-started' },
+          { text: 'Architecture', link: '/guide/architecture' },
+          { text: 'Configuration', link: '/guide/configuration' },
+          { text: 'Database', link: '/guide/database' },
+          { text: 'Deployment', link: '/guide/deployment' }
+        ]
+      },
+      {
+        text: 'API reference',
+        items: [
+          { text: 'REST API', link: '/api/rest' },
+          { text: 'Image engine', link: '/api/image-engine' },
+          { text: 'AI engine', link: '/api/ai' }
+        ]
+      }
+    ],
+
+    socialLinks: [
+      { icon: 'github', link: 'https://github.com/siddharthksah/Stirling-Image' }
+    ],
+
+    search: {
+      provider: 'local'
+    },
+
+    footer: {
+      message: 'Released under the MIT License.',
+    },
+
+    editLink: {
+      pattern: 'https://github.com/siddharthksah/Stirling-Image/edit/main/apps/docs/:path',
+      text: 'Edit this page on GitHub'
+    }
+  }
+})