fix(collab): preserve line breaks in notes display (#608)

Add remark-breaks plugin so single newlines in note content render
as <br> instead of being collapsed by Markdown. Applies to both
the card preview and the expanded view.

client/package-lock.json

@@ -21,6 +21,7 @@
         "react-markdown": "^10.1.0",
         "react-router-dom": "^6.22.2",
         "react-window": "^2.2.7",
+        "remark-breaks": "^4.0.0",
         "remark-gfm": "^4.0.1",
         "topojson-client": "^3.1.0",
         "zustand": "^4.5.2"
@@ -7585,6 +7586,20 @@
         "url": "https://opencollective.com/unified"
       }
     },
+    "node_modules/mdast-util-newline-to-break": {
+      "version": "2.0.0",
+      "resolved": "https://registry.npmjs.org/mdast-util-newline-to-break/-/mdast-util-newline-to-break-2.0.0.tgz",
+      "integrity": "sha512-MbgeFca0hLYIEx/2zGsszCSEJJ1JSCdiY5xQxRcLDDGa8EPvlLPupJ4DSajbMPAnC0je8jfb9TiUATnxxrHUog==",
+      "license": "MIT",
+      "dependencies": {
+        "@types/mdast": "^4.0.0",
+        "mdast-util-find-and-replace": "^3.0.0"
+      },
+      "funding": {
+        "type": "opencollective",
+        "url": "https://opencollective.com/unified"
+      }
+    },
     "node_modules/mdast-util-phrasing": {
       "version": "4.1.0",
       "resolved": "https://registry.npmjs.org/mdast-util-phrasing/-/mdast-util-phrasing-4.1.0.tgz",
@@ -9272,6 +9287,21 @@
         "regjsparser": "bin/parser"
       }
     },
+    "node_modules/remark-breaks": {
+      "version": "4.0.0",
+      "resolved": "https://registry.npmjs.org/remark-breaks/-/remark-breaks-4.0.0.tgz",
+      "integrity": "sha512-IjEjJOkH4FuJvHZVIW0QCDWxcG96kCq7An/KVH2NfJe6rKZU2AsHeB3OEjPNRxi4QC34Xdx7I2KGYn6IpT7gxQ==",
+      "license": "MIT",
+      "dependencies": {
+        "@types/mdast": "^4.0.0",
+        "mdast-util-newline-to-break": "^2.0.0",
+        "unified": "^11.0.0"
+      },
+      "funding": {
+        "type": "opencollective",
+        "url": "https://opencollective.com/unified"
+      }
+    },
     "node_modules/remark-gfm": {
       "version": "4.0.1",
       "resolved": "https://registry.npmjs.org/remark-gfm/-/remark-gfm-4.0.1.tgz",