feat: Modern styling, draw.io integration, and C4 architecture docs

Styling:
- Dark-first design (Vercel/Linear inspired) with Geist font
- Custom CSS with full --ifm- token overrides
- Glassmorphic navbar, refined sidebar, modern tables
- Gradient hero with animated glow, app cards, C4 section
- Custom badge, tag, and callout components
- Announcement bar, TOC config, dark scrollbar

draw.io:
- Added docusaurus-plugin-drawio + raw-loader
- SMP full pipeline diagram (smp-pipeline.drawio)
- Embedded in architecture overview

Mermaid:
- Added @docusaurus/theme-mermaid
- C4Context, C4Container, C4Component diagrams
- Sequence and graph diagrams in architecture

C4 Architecture (Stock Market Professional):
- L1 Context: system in the world, actors, external systems
- L2 Containers: Data Ingestor, Analysis Engine, Signal Generator, TimescaleDB, Notifier
- L3 Components: deep component breakdown with mermaid C4Component diagrams

Other:
- Sidebar restructured with C4 section and Modules section
- Homepage rebuilt as modern dark landing page

docusaurus.config.ts

@@ -4,7 +4,7 @@ import type * as Preset from '@docusaurus/preset-classic';
 
 const config: Config = {
   title: 'SKIC Playground',
-  tagline: 'Documentation for SKIC autonomous applications',
+  tagline: 'Autonomous application documentation',
   favicon: 'img/favicon.ico',
 
   url: 'https://docs.skic-playground.lego-cloud.eu',
@@ -14,26 +14,41 @@ const config: Config = {
   projectName: 'documentation',
 
   onBrokenLinks: 'throw',
-  onBrokenMarkdownLinks: 'warn',
+  markdown: {
+    hooks: {
+      onBrokenMarkdownLinks: 'warn',
+    },
+    mermaid: true,
+  },
 
   i18n: {
     defaultLocale: 'en',
     locales: ['en'],
   },
 
+  themes: [
+    '@docusaurus/theme-mermaid',
+  ],
+
+  plugins: [
+    'docusaurus-plugin-drawio',
+  ],
+
   presets: [
     [
       'classic',
       {
         docs: {
           sidebarPath: './sidebars.ts',
-          editUrl:
-            'https://gitea.lego-cloud.eu/skic-v1-playground/documentation/src/branch/main/',
+          editUrl: 'https://gitea.lego-cloud.eu/skic-v1-playground/documentation/src/branch/main/',
+          showLastUpdateTime: true,
+          showLastUpdateAuthor: true,
         },
         blog: {
           showReadingTime: true,
-          editUrl:
-            'https://gitea.lego-cloud.eu/skic-v1-playground/documentation/src/branch/main/',
+          blogTitle: 'Changelog',
+          blogDescription: 'Updates and changes to SKIC applications',
+          postsPerPage: 'ALL',
         },
         theme: {
           customCss: './src/css/custom.css',
@@ -43,58 +58,78 @@ const config: Config = {
   ],
 
   themeConfig: {
+    colorMode: {
+      defaultMode: 'dark',
+      disableSwitch: false,
+      respectPrefersColorScheme: true,
+    },
+
+    image: 'img/docusaurus-social-card.jpg',
+
+    announcementBar: {
+      id: 'wip',
+      content: '🚧 SKIC Playground is under active development — documentation is being built autonomously.',
+      backgroundColor: '#1a1a2e',
+      textColor: '#818cf8',
+      isCloseable: true,
+    },
+
     navbar: {
       title: 'SKIC Playground',
+      hideOnScroll: true,
       items: [
         {
           type: 'docSidebar',
           sidebarId: 'docsSidebar',
           position: 'left',
-          label: 'Documentation',
-        },
-        {
-          to: '/blog',
-          label: 'Changelog',
-          position: 'left',
+          label: 'Docs',
         },
+
         {
           href: 'https://gitea.lego-cloud.eu/skic-v1-playground',
-          label: 'Gitea',
           position: 'right',
+          className: 'header-gitea-link',
+          'aria-label': 'Gitea repository',
+          label: 'Gitea ↗',
         },
       ],
     },
+
     footer: {
       style: 'dark',
       links: [
         {
-          title: 'Docs',
+          title: 'Documentation',
           items: [
-            {
-              label: 'Getting Started',
-              to: '/docs/intro',
-            },
-            {
-              label: 'Applications',
-              to: '/docs/applications/stock-market-professional',
-            },
+            { label: 'Getting Started', to: '/docs/guides/getting-started' },
+            { label: 'Stock Market Pro', to: '/docs/applications/stock-market-professional' },
+            { label: 'Architecture', to: '/docs/architecture/overview' },
           ],
         },
         {
           title: 'Infrastructure',
           items: [
-            {
-              label: 'Gitea',
-              href: 'https://gitea.lego-cloud.eu/skic-v1-playground',
-            },
+            { label: 'Gitea', href: 'https://gitea.lego-cloud.eu/skic-v1-playground' },
+            { label: 'Keycloak', href: 'https://keycloak.lego-cloud.eu' },
           ],
         },
       ],
-      copyright: `Copyright © ${new Date().getFullYear()} SKIC Playground. Built with Docusaurus.`,
+      copyright: `© ${new Date().getFullYear()} SKIC Playground · Built by Jarvis`,
     },
+
     prism: {
-      theme: prismThemes.github,
-      darkTheme: prismThemes.dracula,
+      theme: prismThemes.oneDark,
+      darkTheme: prismThemes.oneDark,
+      additionalLanguages: ['bash', 'python', 'sql', 'yaml', 'json', 'typescript', 'docker'],
+    },
+
+    mermaid: {
+      theme: { light: 'neutral', dark: 'dark' },
+    },
+
+    tableOfContents: {
+      minHeadingLevel: 2,
+      maxHeadingLevel: 4,
     },
   } satisfies Preset.ThemeConfig,
 };