feat(libs): react load overlay + progress bar; mimalloc mallinfo stub; framed tests

- WasmTool/source.ts: LIB_LOADING_EVENT brackets the fat-load; full-cover
  overlay ('Loading <kind> libraries…') with a per-lib progress bar (done/total
  from listLibs), show-on-first / hide-after-last coalescing.
- mallinfo stub (wasm/shims/mallinfo_stub.c + build-kicad-target.sh): -sMALLOC=
  mimalloc doesn't export glibc mallinfo() that OpenCASCADE OSD_MemInfo (pcbnew
  3D) needs; zeroed no-op unblocks the pcbnew link.
- source/cdn-source tests: updated to the framed Uint8Array 'bodies' contract.
- bump kicad -> e8db3d3.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

wasm/shims/mallinfo_stub.c

@@ -0,0 +1,23 @@
+/*
+ * mallinfo() stub for the mimalloc-allocator build.
+ *
+ * We link with -sMALLOC=mimalloc (per-thread heaps — needed so the parallel
+ * s-expr library parse doesn't serialize on dlmalloc's single global lock; see
+ * docs/features/libs/0013). Unlike emscripten's dlmalloc/emmalloc, mimalloc does
+ * NOT export the glibc memory-report API mallinfo()/mallinfo2(). OpenCASCADE's
+ * OSD_MemInfo.cxx (in libTKernel, linked only by pcbnew for 3D/STEP) references
+ * mallinfo(), so the pcbnew link fails with `undefined symbol: mallinfo` without
+ * this. (eeschema doesn't link OpenCASCADE, so it never needed it.)
+ *
+ * mallinfo() is used purely for optional memory reporting, so a zeroed result is
+ * harmless. Provided unconditionally (mirrors the nanosleep_yield / gl_ffp stub
+ * pattern); it's a no-op for apps that never reference it.
+ */
+
+#include <malloc.h>
+
+struct mallinfo mallinfo( void )
+{
+    struct mallinfo info = { 0 };
+    return info;
+}