feat: Sharp style, Tailwind+shadcn, dark navbar, nav restructure, Go/monorepo guidelines

Styling:
- Tailwind CSS v4 (preflight:false) integrated via PostCSS plugin
- shadcn/ui New York style with --radius:0 (sharp corners everywhere)
- Zero border-radius on ALL elements: buttons, code blocks, cards, admonitions, badges
- Navbar FORCE dark (#0a0a0a) in both light/dark modes via !important
- ThemeSynchronizer: bridges Docusaurus data-theme → shadcn .dark class
- Active sidebar item gets left border accent instead of rounded bg

React UI components (src/components/ui/index.tsx):
- Badge (6 variants: wip, stable, planned, success, warning, outline)
- Card + CardHeader + CardTitle + CardContent
- Callout (note/info/success/warning/danger) - sharp, left-border style
- PropertiesTable - monospace typed API reference tables
- StatusIndicator - operational/degraded/outage/maintenance

Navigation restructure:
- Introduction → Platform → Products → Engineering → Runbooks
- Old 'applications/' removed, moved to products/stock-market-pro/
- New Platform section: infrastructure overview + CI/CD pipeline docs
- New Engineering section: monorepo structure, Go stack, conventions
- New Runbooks section: incident severity, common procedures

Implementation guidelines (engineering/guidelines.md):
- Monorepo layout with go.work workspace
- Go as primary language (why + standard library table)
- Python as sidecar for data/ML workloads
- Code conventions: gofmt, error wrapping, logging, testing
- Git conventions: branch naming, conventional commits
- Makefile targets per app
- How to add a new application (step-by-step)

docs/platform/overview.md

@@ -0,0 +1,43 @@
+---
+sidebar_position: 1
+---
+
+# Platform Overview
+
+SKIC Playground runs entirely on self-hosted infrastructure at `lego-cloud.eu`.
+
+## Infrastructure Diagram
+
+```mermaid
+graph TB
+    subgraph TrueNAS["TrueNAS SCALE 26.0 — lego-cloud.eu"]
+        direction TB
+        Gitea["Gitea 1.26\nSource + CI/CD\ngitea.lego-cloud.eu"]
+        Zot["Zot Registry\n:30264\nOCI images"]
+        Keycloak["Keycloak\nSSO / Auth\nkeycloak.lego-cloud.eu"]
+        Hermes["Hermes Agent\nAI Operations\n(Jarvis)"]
+        Apps["Application\nContainers"]
+    end
+
+    Dev["Developer / Jarvis"] -->|git push| Gitea
+    Gitea -->|Actions runner| CI["CI/CD Worker"]
+    CI -->|docker push| Zot
+    CI -->|deploy| Apps
+    Zot -->|pull| Apps
+    Keycloak -->|auth| Apps
+    Hermes -->|manages| Gitea
+    Hermes -->|manages| Apps
+```
+
+## Services
+
+| Service | URL | Version | Purpose |
+|---|---|---|---|
+| Gitea | gitea.lego-cloud.eu | 1.26.2 | Source control, CI/CD, issue tracking |
+| Keycloak | keycloak.lego-cloud.eu | — | Authentication, SSO |
+| Zot | :30264 | — | OCI-compliant container registry |
+| Hermes | local | — | AI agent (Jarvis) — automation, docs, ops |
+
+## Storage
+
+All persistent data lives under `/mnt/lego-cloud-v1-2025-11-28/` on TrueNAS.