feat: replace sidebar with 21st.dev hover-to-expand component

Use framer-motion animated sidebar from 21st.dev — collapses to icons,
expands on hover. Phosphor icons instead of lucide. Remove old manual
collapse/expand and sidebar-context. Top bar has Pulse logo + user
actions, sidebar below with site picker and nav groups.

package-lock.json

@@ -17,6 +17,7 @@
         "@tanstack/react-virtual": "^3.13.21",
         "@types/d3": "^7.4.3",
         "class-variance-authority": "^0.7.1",
+        "clsx": "^2.1.1",
         "cobe": "^0.6.5",
         "country-flag-icons": "^1.6.4",
         "d3": "^7.9.0",
@@ -36,6 +37,7 @@
         "sonner": "^2.0.7",
         "svg-dotted-map": "^2.0.1",
         "swr": "^2.3.3",
+        "tailwind-merge": "^3.5.0",
         "xlsx": "^0.18.5"
       },
       "devDependencies": {
@@ -1684,6 +1686,16 @@
         "react-dom": ">=18"
       }
     },
+    "node_modules/@ciphera-net/ui/node_modules/tailwind-merge": {
+      "version": "2.6.1",
+      "resolved": "https://registry.npmjs.org/tailwind-merge/-/tailwind-merge-2.6.1.tgz",
+      "integrity": "sha512-Oo6tHdpZsGpkKG88HJ8RR1rg/RdnEkQEfMoEk2x1XRI3F1AxeU+ijRXpiVUF4UbLfcxxRGw6TbUINKYdWVsQTQ==",
+      "license": "MIT",
+      "funding": {
+        "type": "github",
+        "url": "https://github.com/sponsors/dcastil"
+      }
+    },
     "node_modules/@csstools/color-helpers": {
       "version": "6.0.2",
       "resolved": "https://registry.npmjs.org/@csstools/color-helpers/-/color-helpers-6.0.2.tgz",
@@ -14352,9 +14364,9 @@
       "license": "MIT"
     },
     "node_modules/tailwind-merge": {
-      "version": "2.6.1",
-      "resolved": "https://registry.npmjs.org/tailwind-merge/-/tailwind-merge-2.6.1.tgz",
-      "integrity": "sha512-Oo6tHdpZsGpkKG88HJ8RR1rg/RdnEkQEfMoEk2x1XRI3F1AxeU+ijRXpiVUF4UbLfcxxRGw6TbUINKYdWVsQTQ==",
+      "version": "3.5.0",
+      "resolved": "https://registry.npmjs.org/tailwind-merge/-/tailwind-merge-3.5.0.tgz",
+      "integrity": "sha512-I8K9wewnVDkL1NTGoqWmVEIlUcB9gFriAEkXkfCjX5ib8ezGxtR3xD7iZIxrfArjEsH7F1CHD4RFUtxefdqV/A==",
       "license": "MIT",
       "funding": {
         "type": "github",