docs: Write quetza docs

services/docs/content/en/quetza/concepts/_index.md

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+---
+title: Concepts
+weight: 4
+---
+
+
+**Quetza** concepts explain the *Why* and *How* behind the framework's design. These documents cover the underlying philosophy and architectural decisions.
+
+## Key Topics
+
+{{% cards %}}
+  {{< card link="architecture" title="Architecture & Philosophy" icon="scale" subtitle="Design principles: Convention over Configuration, Composition, and Isolation." >}}
+  {{< card link="module-system" title="The Module System" icon="template" subtitle="Understanding Clients, Modules, Controllers, and Events." >}}
+{{% /cards %}}