Add experiments folder. Add usage.md and SKILL.md. Fix Sheet interactions and add dynamic sheet mode.

experiments/router-guard-history/README.md

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+# Vue Router guard/history experiment
+
+This small app compares the browser's current URL and history position with
+Vue Router's `currentRoute` while a real `beforeResolve` guard is pending.
+
+## Run it
+
+From the repository root:
+
+```sh
+npm --prefix experiments/router-guard-history run dev
+```
+
+Open the URL printed by Vite.
+
+## Suggested tests
+
+### Forward navigation
+
+1. Enable **Pause the next `beforeResolve`**.
+2. Click **Push Alpha**.
+3. While paused, compare **Browser URL** with **router.currentRoute**.
+4. Allow or reject the navigation.
+
+For `router.push()`, both values remain on the outgoing route until the guard
+allows confirmation.
+
+### Back navigation
+
+1. Push **Alpha**, then push **Beta**.
+2. Enable **Pause the next `beforeResolve`**.
+3. Click **Router Back**.
+4. While paused, compare **Browser URL** with **router.currentRoute**.
+5. Reject the navigation and watch the browser restore its previous history
+   entry, or repeat the test and allow it.
+
+The event timeline separately records the raw browser `popstate`, Vue Router
+guards, the URL, `currentRoute`, and the navigation result.