Update the /api/create endpoint to use JSON (#7935)

Replaces `POST /api/create` to use JSON instead of a Modelfile.

This is a breaking change.

parser/expandpath_test.go

@@ -0,0 +1,57 @@
+package parser
+
+import (
+	"os"
+	"os/user"
+	"path/filepath"
+	"testing"
+)
+
+func TestExpandPath(t *testing.T) {
+	mockCurrentUser := func() (*user.User, error) {
+		return &user.User{
+			Username: "testuser",
+			HomeDir:  "/home/testuser",
+		}, nil
+	}
+
+	mockLookupUser := func(username string) (*user.User, error) {
+		fakeUsers := map[string]string{
+			"testuser":    "/home/testuser",
+			"anotheruser": "/home/anotheruser",
+		}
+
+		if homeDir, ok := fakeUsers[username]; ok {
+			return &user.User{
+				Username: username,
+				HomeDir:  homeDir,
+			}, nil
+		}
+		return nil, os.ErrNotExist
+	}
+
+	tests := []struct {
+		input           string
+		expected        string
+		windowsExpected string
+		shouldErr       bool
+	}{
+		{"~", "/home/testuser", "D:\\home\\testuser", false},
+		{"~/myfolder/myfile.txt", "/home/testuser/myfolder/myfile.txt", "D:\\home\\testuser\\myfolder\\myfile.txt", false},
+		{"~anotheruser/docs/file.txt", "/home/anotheruser/docs/file.txt", "D:\\home\\anotheruser\\docs\\file.txt", false},
+		{"~nonexistentuser/file.txt", "", "", true},
+		{"relative/path/to/file", filepath.Join(os.Getenv("PWD"), "relative/path/to/file"), "relative\\path\\to\\file", false},
+		{"/absolute/path/to/file", "/absolute/path/to/file", "D:\\absolute\\path\\to\\file", false},
+		{".", os.Getenv("PWD"), os.Getenv("PWD"), false},
+	}
+
+	for _, test := range tests {
+		result, err := expandPathImpl(test.input, mockCurrentUser, mockLookupUser)
+		if (err != nil) != test.shouldErr {
+			t.Errorf("expandPathImpl(%q) returned error: %v, expected error: %v", test.input, err != nil, test.shouldErr)
+		}
+		if result != test.expected && result != test.windowsExpected && !test.shouldErr {
+			t.Errorf("expandPathImpl(%q) = %q, want %q", test.input, result, test.expected)
+		}
+	}
+}