Add runtime resource loading and fix Docker incremental builds

- Build images.tar.gz bitmap archive for KiCad icons
- Fetch resources at runtime via HTTP instead of bundling in WASM
- Write to Emscripten virtual FS at compile-time KICAD_DATA path
- Fix rsync timestamp handling for correct make change detection
- Update kicad submodule with WASM settings manager fix

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

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

scripts/kicad/build-pcbnew.sh

@@ -306,6 +306,11 @@ fi
 log_info "Building pcbnew..."
 emmake make -j${JOBS} pcbnew
 
+# Step 8.1: Build bitmap resources (images.tar.gz)
+# This creates the icon archive that KiCad loads at runtime
+log_info "Building bitmap resources..."
+emmake make bitmap_archive_build
+
 # Step 9: Create stamp file
 create_stamp "${KICAD_STAMP}"
 log_info "KiCad PCBnew build complete!"