reorganize: consolidate demo directories

- Consolidate _demo, _pydemo, _embdemo into single _demo directory structure
- Organize demos by language: _demo/{go,py,c,embed}/
- Categorize demos based on imports:
- Python library demos (py imports) → _demo/py/
- C/C++ library demos (c/cpp imports) → _demo/c/
- Go-specific demos → _demo/go/
- Embedded demos → _demo/embed/
- Move C-related demos (asm*, cabi*, cgo*, linkname, targetsbuild) from go/ to c/
- Update all path references in README.md and GitHub workflows
- Improve demo organization and navigation as requested in #1256

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

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

_demo/c/socket/server/server.go

@@ -0,0 +1,43 @@
+package main
+
+import (
+	"unsafe"
+
+	"github.com/goplus/lib/c"
+	"github.com/goplus/lib/c/net"
+	"github.com/goplus/lib/c/os"
+)
+
+func main() {
+	var buffer [256]c.Char
+
+	sockfd := net.Socket(net.AF_INET, net.SOCK_STREAM, 0)
+	defer os.Close(sockfd)
+
+	servAddr := &net.SockaddrIn{
+		Family: net.AF_INET,
+		Port:   net.Htons(uint16(1234)),
+		Addr:   net.InAddr{Addr: 0x00000000},
+		Zero:   [8]c.Char{0, 0, 0, 0, 0, 0, 0, 0},
+	}
+	if res := net.Bind(sockfd, servAddr, c.Uint(unsafe.Sizeof(*servAddr))); res < 0 {
+		c.Perror(c.Str("bind error"))
+		return
+	}
+
+	if net.Listen(sockfd, 5) < 0 {
+		c.Printf(c.Str("listen error"))
+		return
+	}
+	c.Printf(c.Str("Listening on port 1234...\n"))
+
+	cliAddr, clilen := &net.SockaddrIn{}, c.Uint(unsafe.Sizeof(servAddr))
+
+	newsockfd := net.Accept(sockfd, cliAddr, &clilen)
+	defer os.Close(newsockfd)
+	c.Printf(c.Str("Connection accepted."))
+
+	os.Read(newsockfd, unsafe.Pointer(unsafe.SliceData(buffer[:])), 256)
+	c.Printf(c.Str("Received: %s"), &buffer[0])
+
+}