Implement multi-platform build system with pure Go support

- Introduced a comprehensive build system that supports multiple platforms (Linux, macOS, Windows, Android) using pure Go builds (`CGO_ENABLED=0`).
- Updated all build and test scripts to ensure compatibility with the new purego approach, allowing for dynamic loading of `libsecp256k1` at runtime.
- Added detailed documentation on the build process, platform detection, and deployment options.
- Enhanced CI/CD workflows to automate builds for all supported platforms and include necessary libraries in releases.
- Updated `.gitignore` to exclude build output files.
- Created new documentation files for deployment and multi-platform build summaries.

scripts/test-deploy-local.sh

@@ -162,8 +162,13 @@ else
 fi
 
 echo -e "${YELLOW}8. Testing build capability...${NC}"
-if go build -o "$temp_dir/test-orly" . >/dev/null 2>&1; then
-    echo -e "${GREEN}✓ Project builds successfully${NC}"
+if CGO_ENABLED=0 go build -o "$temp_dir/test-orly" . >/dev/null 2>&1; then
+    echo -e "${GREEN}✓ Project builds successfully (pure Go + purego)${NC}"
+    # Copy libsecp256k1.so if available (runtime optional)
+    if [[ -f "pkg/crypto/p8k/libsecp256k1.so" ]]; then
+        cp pkg/crypto/p8k/libsecp256k1.so "$temp_dir/"
+        echo -e "${GREEN}✓ libsecp256k1.so copied (runtime optional)${NC}"
+    fi
     if [[ -x "$temp_dir/test-orly" ]]; then
         echo -e "${GREEN}✓ Binary is executable${NC}"
     else