Refactor math chapter structure and styling: Update .gitignore to exclude specific CSS directories, enhance CONTRIBUTING.md with new guidelines for subject-specific assets, and streamline chapter content organization. Modify curriculum data to include new chapter dependencies and improve frontend logic for loading shared styles and scripts. Adjust styles for better visual consistency across math chapters.

data/math-curriculum.json

@@ -3,6 +3,10 @@
   "intro": "Topic units across three strands, shaped for learners worldwide. The map shows required prerequisites; the list follows a readable teaching order; Compare explains how chapters relate to popular curricula.",
   "graph": {
     "edges": [
+      {
+        "from": "zero-and-one",
+        "to": "counting-and-numbers"
+      },
       {
         "from": "counting-and-numbers",
         "to": "basic-math-notation"
@@ -206,10 +210,28 @@
       "id": "number-algebra",
       "title": "Number & Algebra",
       "chapters": [
+        {
+          "slug": "zero-and-one",
+          "title": "Zero and one",
+          "description": "0 is nothing; 1 is one. Learn to tell them apart — the same skill as telling false from true — before counting larger amounts.",
+          "status": "live",
+          "curriculumCoverage": {
+            "Foundation": "core",
+            "IGCSE": "core",
+            "Common Core": "core",
+            "Singapore": "core",
+            "UK GCSE": "core",
+            "DSE": "related",
+            "IB": "related",
+            "A-Level": "related",
+            "AP": "related",
+            "Gaokao": "related"
+          }
+        },
         {
           "slug": "counting-and-numbers",
           "title": "Counting and numbers",
-          "description": "Count from zero, spot patterns, add, multiply, and divide; then meet place value and big numbers from hundreds to billions.",
+          "description": "Count objects, spot patterns, add, multiply, and divide; then meet place value and big numbers from hundreds to billions.",
           "status": "live",
           "curriculumCoverage": {
             "Foundation": "core",