Improve build system with debug symbols, clean modes, and parallel jobs

- Add build.md documentation for the WASM build system
- Default to debug builds with -gsource-map for WASM debugging
- Add --release flag to disable debug symbols
- Add --clean flag for full rebuild (deps + wxWidgets + KiCad)
- Add -j N flag for parallel compilation (default: 1 for sequential)
- Update Docker memory limit to 32GB
- Propagate DEBUG_BUILD and JOBS to all dependency scripts

Build modes:
- ./docker/build.sh --clean -j8  (full rebuild, parallel)
- ./docker/build.sh              (rebuild KiCad only)
- ./docker/build.sh --no-clean   (incremental)

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docker/docker-compose.yml

@@ -5,12 +5,12 @@ services:
       dockerfile: docker/Dockerfile
     container_name: kicad-wasm-builder
 
-    # Resource limits (M4 Max: 10 cores, 16GB)
+    # Resource limits (adjust based on your machine)
     deploy:
       resources:
         limits:
           cpus: '10'
-          memory: 16G
+          memory: 32G
 
     volumes:
       # Source code (read-write for git operations)