feat: refresh UI with new typography and edit diff display (#63)

- Switch from Geist to Plus Jakarta Sans (body) and JetBrains Mono (code)
- Add visual diff display for edit_diagram tool showing search/replace pairs
- Update color palette to clean modern OKLCH-based scheme
- Improve chat message display with better styling and animations
- Add syntax-highlighted code blocks for XML/JSON output
- Improve scrollbar and shadow utilities

package-lock.json

@@ -32,6 +32,7 @@
                 "next": "15.2.3",
                 "ollama-ai-provider-v2": "^1.5.4",
                 "pako": "^2.1.0",
+                "prism-react-renderer": "^2.4.1",
                 "react": "^19.0.0",
                 "react-dom": "^19.0.0",
                 "react-drawio": "^1.0.3",
@@ -2792,6 +2793,12 @@
             "dev": true,
             "license": "MIT"
         },
+        "node_modules/@types/prismjs": {
+            "version": "1.26.5",
+            "resolved": "https://registry.npmjs.org/@types/prismjs/-/prismjs-1.26.5.tgz",
+            "integrity": "sha512-AUZTa7hQ2KY5L7AmtSiqxlhWxb4ina0yd8hNbl4TWuqnv/pFP0nDMb3YrfSBf4hJVGLh2YEIBfKaBW/9UEl6IQ==",
+            "license": "MIT"
+        },
         "node_modules/@types/react": {
             "version": "19.1.0",
             "resolved": "https://registry.npmjs.org/@types/react/-/react-19.1.0.tgz",
@@ -7867,6 +7874,19 @@
                 "node": ">= 0.8.0"
             }
         },
+        "node_modules/prism-react-renderer": {
+            "version": "2.4.1",
+            "resolved": "https://registry.npmjs.org/prism-react-renderer/-/prism-react-renderer-2.4.1.tgz",
+            "integrity": "sha512-ey8Ls/+Di31eqzUxC46h8MksNuGx/n0AAC8uKpwFau4RPDYLuE3EXTp8N8G2vX2N7UC/+IXeNUnlWBGGcAG+Ig==",
+            "license": "MIT",
+            "dependencies": {
+                "@types/prismjs": "^1.26.0",
+                "clsx": "^2.0.0"
+            },
+            "peerDependencies": {
+                "react": ">=16.0.0"
+            }
+        },
         "node_modules/prop-types": {
             "version": "15.8.1",
             "resolved": "https://registry.npmjs.org/prop-types/-/prop-types-15.8.1.tgz",