quality: add quality system overview

Author: OgeonX-Ai

docs/quality-system/README.md

@@ -0,0 +1,26 @@
+# Quality System
+
+AI-OS quality is based on evidence, not confidence.
+
+## Quality loop
+
+```mermaid
+flowchart TD
+    A[Change] --> B[Structure check]
+    B --> C[Link check]
+    C --> D[Diagram check]
+    D --> E[Policy check]
+    E --> F{Pass?}
+    F -- No --> G[Improve]
+    G --> B
+    F -- Yes --> H[Ready]
+```
+
+## Quality gates
+
+- required files exist
+- Markdown files have titles
+- key docs include Mermaid diagrams
+- relative links resolve
+- work-marker text is not left in docs
+- CI can run the verifier