Update contributing guidelines and enhance build scripts: Add detailed instructions for build modes in CONTRIBUTING.md, clarifying the use of incremental and full rebuilds. Revise package.json to streamline build commands and introduce new dev scripts for better development workflow. Remove deprecated integer arithmetic chapter files and update curriculum JSON to reflect the latest structure. Enhance Pythagorean theorem content with a new vocabulary section for improved clarity.

data/math-curriculum.json

@@ -29,7 +29,7 @@
       },
       {
         "from": "integer-foundations",
-        "to": "integer-arithmetic"
+        "to": "polynomials-expansion-factorisation"
       },
       {
         "from": "rational-number-operations",
@@ -43,10 +43,6 @@
         "from": "percentage-applications",
         "to": "ratios-and-rates-foundation"
       },
-      {
-        "from": "integer-arithmetic",
-        "to": "polynomials-expansion-factorisation"
-      },
       {
         "from": "polynomials-expansion-factorisation",
         "to": "algebraic-fractions-formulas"
@@ -310,24 +306,6 @@
             "Gaokao": "related"
           }
         },
-        {
-          "slug": "integer-arithmetic",
-          "title": "Integer arithmetic",
-          "description": "Multiply and divide integers from models to symbolic rules; apply order of operations with signed numbers in multi-step expressions.",
-          "status": "live",
-          "curriculumCoverage": {
-            "Foundation": "core",
-            "IGCSE": "core",
-            "Common Core": "core",
-            "Singapore": "core",
-            "UK GCSE": "core",
-            "IB": "related",
-            "A-Level": "related",
-            "AP": "related",
-            "DSE": "related",
-            "Gaokao": "related"
-          }
-        },
         {
           "slug": "rational-number-operations",
           "title": "Fractions and decimals",