Add GitHub-style callout support

Implement proper GitHub-style callouts with beautiful styling:

Features:
- Custom rehype plugin to transform > [!NOTE] syntax
- Support for 5 callout types:
  * NOTE (blue, 📝)
  * TIP (green, 💡)
  * IMPORTANT (purple, ❗)
  * WARNING (orange, ⚠️)
  * CAUTION (red, 🚨)
- Gradient backgrounds with accent colors
- Full dark mode support
- Converts existing emoji callouts to proper format

Files:
- lib/rehype-callouts.ts: Custom plugin for parsing
- contentlayer.config.ts: Add plugin to pipeline
- styles/globals.css: Beautiful styling for all types
- content/: Convert 2 emoji callouts to [!TIP] format

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

package-lock.json

@@ -28,6 +28,7 @@
         "rehype-autolink-headings": "^7.1.0",
         "rehype-pretty-code": "^0.14.1",
         "rehype-slug": "^6.0.0",
+        "remark-directive": "^4.0.0",
         "remark-gfm": "^4.0.1",
         "shiki": "^3.15.0",
         "tailwind-merge": "^3.4.0",
@@ -7355,6 +7356,27 @@
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       }
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+      "license": "MIT",
+      "dependencies": {
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+        "@types/unist": "^3.0.0",
+        "ccount": "^2.0.0",
+        "devlop": "^1.0.0",
+        "mdast-util-from-markdown": "^2.0.0",
+        "mdast-util-to-markdown": "^2.0.0",
+        "parse-entities": "^4.0.0",
+        "stringify-entities": "^4.0.0",
+        "unist-util-visit-parents": "^6.0.0"
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+        "url": "https://opencollective.com/unified"
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@@ -7804,6 +7826,25 @@
         "micromark-util-types": "^2.0.0"
       }
     },
+    "node_modules/micromark-extension-directive": {
+      "version": "4.0.0",
+      "resolved": "https://registry.npmjs.org/micromark-extension-directive/-/micromark-extension-directive-4.0.0.tgz",
+      "integrity": "sha512-/C2nqVmXXmiseSSuCdItCMho7ybwwop6RrrRPk0KbOHW21JKoCldC+8rFOaundDoRBUWBnJJcxeA/Kvi34WQXg==",
+      "license": "MIT",
+      "dependencies": {
+        "devlop": "^1.0.0",
+        "micromark-factory-space": "^2.0.0",
+        "micromark-factory-whitespace": "^2.0.0",
+        "micromark-util-character": "^2.0.0",
+        "micromark-util-symbol": "^2.0.0",
+        "micromark-util-types": "^2.0.0",
+        "parse-entities": "^4.0.0"
+      },
+      "funding": {
+        "type": "opencollective",
+        "url": "https://opencollective.com/unified"
+      }
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     "node_modules/micromark-extension-frontmatter": {
       "version": "2.0.0",
       "resolved": "https://registry.npmjs.org/micromark-extension-frontmatter/-/micromark-extension-frontmatter-2.0.0.tgz",
@@ -9712,6 +9753,22 @@
         "url": "https://opencollective.com/unified"
       }
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+    "node_modules/remark-directive": {
+      "version": "4.0.0",
+      "resolved": "https://registry.npmjs.org/remark-directive/-/remark-directive-4.0.0.tgz",
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+      "license": "MIT",
+      "dependencies": {
+        "@types/mdast": "^4.0.0",
+        "mdast-util-directive": "^3.0.0",
+        "micromark-extension-directive": "^4.0.0",
+        "unified": "^11.0.0"
+      },
+      "funding": {
+        "type": "opencollective",
+        "url": "https://opencollective.com/unified"
+      }
+    },
     "node_modules/remark-frontmatter": {
       "version": "5.0.0",
       "resolved": "https://registry.npmjs.org/remark-frontmatter/-/remark-frontmatter-5.0.0.tgz",