docs: add usage and developer documentation

Add user and developer documentation plus Pagenary docsite publishing support.

Includes Getting Started, Developer Guide, API and MCP references, Pagenary tenant metadata, npm scripts for sync/build/check/serve, and validation coverage for the generated docsite.

Closes #102

tenants.json

@@ -0,0 +1,19 @@
+{
+  "tenants": [
+    {
+      "id": "t3mp3st-docs",
+      "source": {
+        "type": "local",
+        "path": "./docsite/t3mp3st-docs"
+      },
+      "strictLinks": true,
+      "language": "en-US",
+      "accessibility": {
+        "strict": false,
+        "report": {
+          "enabled": true
+        }
+      }
+    }
+  ]
+}