docs: auto-inject version from VERSION.txt into Doxyfile

PROJECT_NUMBER was hardcoded 3.0.0. Now uses 0.0.0-dev placeholder,
docs.yml injects actual version from VERSION.txt before doxygen runs.

.github/workflows/docs.yml

@@ -33,6 +33,12 @@ jobs:
           sudo apt-get update -qq
           sudo apt-get install -y doxygen
 
+      - name: Inject version into Doxyfile
+        run: |
+          VERSION=$(cat VERSION.txt 2>/dev/null || echo "dev")
+          sed -i "s/^PROJECT_NUMBER.*/PROJECT_NUMBER         = ${VERSION}/" Doxyfile
+          echo "Doxyfile PROJECT_NUMBER = ${VERSION}"
+
       - name: Generate documentation
         run: doxygen Doxyfile
 

Doxyfile

@@ -6,7 +6,7 @@
 # ============================================================================
 
 PROJECT_NAME           = "UltrafastSecp256k1"
-PROJECT_NUMBER         = 3.0.0
+PROJECT_NUMBER         = 0.0.0-dev
 PROJECT_BRIEF          = "Ultra high-performance secp256k1 elliptic curve cryptography library"
 PROJECT_LOGO           =