Use GuessMimeType for mime based completion

complete_by_mimepat called mime.TypeByExtension directly, so it saw only the
extensions the Go standard library knows about. Everything else in kitty that
needs a mime type goes through utils.GuessMimeType, which also consults the
user's mime.types, kitty's builtin types and KnownExtensions. As a result
files like foo.py or foo.toml were not offered when completing arguments that
ask for text/*, even though kitten pager opens them as text.

tools/cli/files.go

@@ -4,7 +4,6 @@ package cli
 
 import (
 	"fmt"
-	"mime"
 	"os"
 	"path/filepath"
 	"slices"
@@ -191,16 +190,7 @@ func complete_by_mimepat(prefix, cwd string, patterns []string) []string {
 		if all_allowed {
 			return true
 		}
-		idx := strings.Index(name, ".")
-		if idx < 1 {
-			return false
-		}
-		ext := name[idx:]
-		mt := mime.TypeByExtension(ext)
-		if mt == "" {
-			ext = filepath.Ext(name)
-			mt = mime.TypeByExtension(ext)
-		}
+		mt := utils.GuessMimeType(name)
 		if mt == "" {
 			return false
 		}

tools/cli/files_test.go

@@ -124,6 +124,20 @@ func TestCompleteFiles(t *testing.T) {
 	if !found {
 		t.Fatalf("Directory containing only an uppercase extension match not completed by FnmatchCompleter: %#v", c.Groups)
 	}
+
+	// mime types kitty knows about but the Go stdlib does not
+	create("zz.py")
+	c = NewCompletions()
+	MimepatCompleter("", CWD, "text/*")(c, "zz", 0)
+	found = false
+	for _, g := range c.Groups {
+		for _, m := range g.Matches {
+			found = found || m.Word == "zz.py"
+		}
+	}
+	if !found {
+		t.Fatalf("File with a mime type known only to kitty not completed by MimepatCompleter: %#v", c.Groups)
+	}
 }
 
 func TestCompleteExecutables(t *testing.T) {