Add designlang public-shell pack; tighten auth capture checks

Ran authenticated extract against coulomb.social; session metadata
matched anonymous Bubble defaults, so treat docs/design-extract as a
public shell baseline (PROVENANCE.md). Capture script now refuses to
overwrite storage-state.json with thin anonymous sessions.

docs/design-extract/prompts/recipes/button.md

@@ -0,0 +1,28 @@
+# Recipe: button
+Build one button component that matches this brand.
+Palette: #000000, #171717, #d08728, #ffffff, #616161, #e5e5e5
+Typography: [object Object], [object Object], [object Object], [object Object]
+Material: flat
+Signals: Radius: 4, 8 · Shadows: rgb(97, 97, 97) 2px 2px 8px 0px
+## Anatomy (detected)
+```json
+{
+  "kind": "button",
+  "structuralHash": "button>svg",
+  "instanceCount": 1,
+  "variants": [
+    {
+      "css": {
+        "background": "rgba(0, 0, 0, 0)",
+        "color": "rgb(208, 135, 40)",
+        "padding": "5px 5px 5px 5px",
+        "borderRadius": "4px",
+        "border": "0px none rgb(208, 135, 40)",
+        "fontSize": "13.3333px",
+        "fontWeight": "400"
+      },
+      "instanceCount": 1
+    }
+  ]
+}
+```