Enable 3D viewer in KiCad WASM build

Build the 3D viewer code for WASM instead of stubbing it out.
This is simpler to maintain than complex header stubs.

Changes:
- Enable KICAD_BUILD_3D_VIEWER_WASM=ON in build script
- Remove -gsource-map to avoid OOM in wasm-emscripten-finalize
- Add OpenGL stubs for fixed-function pipeline (WebGL ES 2.0 only)
- Add GLU stub for gluErrorString
- Add NNG stub for IPC API (sockets don't work in WASM)
- Add PCBnew scripting stub
- Expand curl and libgit2 stubs

The 3D viewer code compiles but won't render at runtime since
OpenGL GAL is disabled and Cairo GAL is used instead.

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

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

wasm/stubs/nng/nng.h

@@ -0,0 +1,47 @@
+/*
+ * NNG stub header for KiCad WASM build
+ * Socket-based IPC is not supported in browsers, so we provide stub implementations
+ * that compile but don't do anything.
+ */
+
+#ifndef NNG_NNG_H
+#define NNG_NNG_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// Error codes
+#define NNG_ETIMEDOUT 5
+#define NNG_ECLOSED   6
+#define NNG_ENOENT    7
+
+// Options
+#define NNG_OPT_RECVTIMEO "recv-timeout"
+
+// Flags
+#define NNG_FLAG_ALLOC 1
+
+// Opaque types
+typedef struct nng_socket_s { int id; } nng_socket;
+typedef struct nng_listener_s { int id; } nng_listener;
+typedef int nng_duration;
+
+// NNG function stubs - all return error codes indicating "not supported"
+int nng_rep0_open(nng_socket *s);
+int nng_listener_create(nng_listener *l, nng_socket s, const char *url);
+int nng_socket_set_ms(nng_socket s, const char *opt, nng_duration dur);
+int nng_listener_start(nng_listener l, int flags);
+int nng_recv(nng_socket s, void *data, size_t *sizep, int flags);
+int nng_send(nng_socket s, void *data, size_t size, int flags);
+int nng_close(nng_socket s);
+void nng_free(void *ptr, size_t size);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif // NNG_NNG_H

wasm/stubs/nng/protocol/reqrep0/rep.h

@@ -0,0 +1,12 @@
+/*
+ * NNG REP protocol stub header for KiCad WASM build
+ */
+
+#ifndef NNG_PROTOCOL_REQREP0_REP_H
+#define NNG_PROTOCOL_REQREP0_REP_H
+
+#include "../../nng.h"
+
+// nng_rep0_open is already declared in nng.h
+
+#endif // NNG_PROTOCOL_REQREP0_REP_H