feat: scroll to post bubble from recommended card + back-to-top button

Recommended cards already routed to /browse#post-<id>, but the stream had
no logic to scroll to the target bubble — and the post might not be paged
in yet. MessageStream now resolves the #post-<id> hash, auto-loads more
pages until the bubble renders, scrolls to it, and gives it a brief gold
highlight. Bubbles get scroll-mt so they clear the sticky header.

Also adds a global floating back-to-top button (BackToTop) mounted in
PublicLayout, shown after scrolling past 400px.

Bundles related staging UI work already present in the working tree.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

package-lock.json

@@ -8,7 +8,7 @@
       "name": "ark-database-web",
       "version": "1.0.0",
       "dependencies": {
-        "animate.css": "^4.1.1",
+        "framer-motion": "^11.18.2",
         "lucide-react": "^0.460.0",
         "react": "^18.3.1",
         "react-dom": "^18.3.1",
@@ -1722,12 +1722,6 @@
         "url": "https://opencollective.com/vitest"
       }
     },
-    "node_modules/animate.css": {
-      "version": "4.1.1",
-      "resolved": "https://registry.npmjs.org/animate.css/-/animate.css-4.1.1.tgz",
-      "integrity": "sha512-+mRmCTv6SbCmtYJCN4faJMNFVNN5EuCTTprDTAo7YzIGji2KADmakjVA3+8mVDkZ2Bf09vayB35lSQIex2+QaQ==",
-      "license": "MIT"
-    },
     "node_modules/ansi-regex": {
       "version": "5.0.1",
       "resolved": "https://registry.npmjs.org/ansi-regex/-/ansi-regex-5.0.1.tgz",
@@ -2360,6 +2354,33 @@
         "url": "https://github.com/sponsors/rawify"
       }
     },
+    "node_modules/framer-motion": {
+      "version": "11.18.2",
+      "resolved": "https://registry.npmjs.org/framer-motion/-/framer-motion-11.18.2.tgz",
+      "integrity": "sha512-5F5Och7wrvtLVElIpclDT0CBzMVg3dL22B64aZwHtsIY8RB4mXICLrkajK4G9R+ieSAGcgrLeae2SeUTg2pr6w==",
+      "license": "MIT",
+      "dependencies": {
+        "motion-dom": "^11.18.1",
+        "motion-utils": "^11.18.1",
+        "tslib": "^2.4.0"
+      },
+      "peerDependencies": {
+        "@emotion/is-prop-valid": "*",
+        "react": "^18.0.0 || ^19.0.0",
+        "react-dom": "^18.0.0 || ^19.0.0"
+      },
+      "peerDependenciesMeta": {
+        "@emotion/is-prop-valid": {
+          "optional": true
+        },
+        "react": {
+          "optional": true
+        },
+        "react-dom": {
+          "optional": true
+        }
+      }
+    },
     "node_modules/fsevents": {
       "version": "2.3.3",
       "resolved": "https://registry.npmjs.org/fsevents/-/fsevents-2.3.3.tgz",
@@ -2774,6 +2795,21 @@
         "node": ">=4"
       }
     },
+    "node_modules/motion-dom": {
+      "version": "11.18.1",
+      "resolved": "https://registry.npmjs.org/motion-dom/-/motion-dom-11.18.1.tgz",
+      "integrity": "sha512-g76KvA001z+atjfxczdRtw/RXOM3OMSdd1f4DL77qCTF/+avrRJiawSG4yDibEQ215sr9kpinSlX2pCTJ9zbhw==",
+      "license": "MIT",
+      "dependencies": {
+        "motion-utils": "^11.18.1"
+      }
+    },
+    "node_modules/motion-utils": {
+      "version": "11.18.1",
+      "resolved": "https://registry.npmjs.org/motion-utils/-/motion-utils-11.18.1.tgz",
+      "integrity": "sha512-49Kt+HKjtbJKLtgO/LKj9Ld+6vw9BjH5d9sc40R/kVyH8GLAXgT42M2NnuPcJNuA3s9ZfZBUcwIgpmZWGEE+hA==",
+      "license": "MIT"
+    },
     "node_modules/ms": {
       "version": "2.1.3",
       "resolved": "https://registry.npmjs.org/ms/-/ms-2.1.3.tgz",
@@ -3728,6 +3764,12 @@
       "dev": true,
       "license": "Apache-2.0"
     },
+    "node_modules/tslib": {
+      "version": "2.8.1",
+      "resolved": "https://registry.npmjs.org/tslib/-/tslib-2.8.1.tgz",
+      "integrity": "sha512-oJFu94HQb+KVduSUQL7wnpmqnfmLsOA/nAh6b6EH0wCEoK0/mPeXU6c3wKDV83MkOuHPRHtSXKKU99IBazS/2w==",
+      "license": "0BSD"
+    },
     "node_modules/typescript": {
       "version": "5.9.3",
       "resolved": "https://registry.npmjs.org/typescript/-/typescript-5.9.3.tgz",