feat: add per-mapping --allow-fallback for layout-independent shortcuts

Add --allow-fallback option to the map command that controls shifted
and ascii (alternate_key) fallback for individual key mappings.

For non-Latin keyboard layouts, when the current layout key is
non-ascii (codepoint > 127 and < 0xE000), the alternate_key from
the base layout is used for matching if the mapping opts in via
--allow-fallback=shifted,ascii.

Default kitty bindings use --allow-fallback=shifted,ascii so they
work out of the box with non-Latin layouts. User custom mappings
default to --allow-fallback=shifted (preserving existing shifted_key
behavior without ascii fallback).

--allow-fallback=none disables all fallback for a mapping.

Python side: parse_options_for_map() in options/utils.py handles flag
parsing, ShortcutMapping uses it in __init__. get_shortcut() filters
candidates by per-mapping allow_fallback.

Go side: ParseMap() handles --allow-fallback, KeyAction stores
AllowFallback, ShortcutTracker.Match passes it to matching.
MatchesParsedShortcut defaults to shifted,ascii for hardcoded shortcuts.

Migrated kittens (themes, command_palette, diff, choose_files) to
use ShortcutTracker with configurable map entries.

Tests added for Python (5 test methods) and Go (ParseMap + key matching).

tools/config/utils_test.go

@@ -28,6 +28,140 @@ func TestStringLiteralParsing(t *testing.T) {
 	}
 }
 
+func TestParseMap(t *testing.T) {
+	// Test without --allow-fallback (default "shifted")
+	ka, err := ParseMap("ctrl+c copy_to_clipboard")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if ka.AllowFallback != "shifted" {
+		t.Fatalf("Expected AllowFallback 'shifted', got %#v", ka.AllowFallback)
+	}
+	if ka.Name != "copy_to_clipboard" {
+		t.Fatalf("Expected Name 'copy_to_clipboard', got %#v", ka.Name)
+	}
+	if diff := cmp.Diff([]string{"ctrl+c"}, ka.Normalized_keys); diff != "" {
+		t.Fatalf("Keys mismatch:\n%s", diff)
+	}
+
+	// Test with --allow-fallback=ascii
+	ka, err = ParseMap("--allow-fallback=ascii ctrl+c copy_to_clipboard")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if ka.AllowFallback != "ascii" {
+		t.Fatalf("Expected AllowFallback 'ascii', got %#v", ka.AllowFallback)
+	}
+	if ka.Name != "copy_to_clipboard" {
+		t.Fatalf("Expected Name 'copy_to_clipboard', got %#v", ka.Name)
+	}
+
+	// Test with --allow-fallback=shifted,ascii
+	ka, err = ParseMap("--allow-fallback=shifted,ascii cmd+c copy_to_clipboard")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if ka.AllowFallback != "shifted,ascii" {
+		t.Fatalf("Expected AllowFallback 'shifted,ascii', got %#v", ka.AllowFallback)
+	}
+	if ka.Name != "copy_to_clipboard" {
+		t.Fatalf("Expected Name 'copy_to_clipboard', got %#v", ka.Name)
+	}
+	if diff := cmp.Diff([]string{"super+c"}, ka.Normalized_keys); diff != "" {
+		t.Fatalf("Keys mismatch:\n%s", diff)
+	}
+
+	// Test with --allow-fallback and action args
+	ka, err = ParseMap("--allow-fallback=shifted,ascii ctrl+shift+f launch --type=tab grep")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if ka.AllowFallback != "shifted,ascii" {
+		t.Fatalf("Expected AllowFallback 'shifted,ascii', got %#v", ka.AllowFallback)
+	}
+	if ka.Name != "launch" {
+		t.Fatalf("Expected Name 'launch', got %#v", ka.Name)
+	}
+	if ka.Args != "--type=tab grep" {
+		t.Fatalf("Expected Args '--type=tab grep', got %#v", ka.Args)
+	}
+
+	// Test space form: --allow-fallback ascii (without =)
+	ka, err = ParseMap("--allow-fallback ascii ctrl+c copy_to_clipboard")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if ka.AllowFallback != "ascii" {
+		t.Fatalf("Expected AllowFallback 'ascii', got %#v", ka.AllowFallback)
+	}
+	if ka.Name != "copy_to_clipboard" {
+		t.Fatalf("Expected Name 'copy_to_clipboard', got %#v", ka.Name)
+	}
+	if diff := cmp.Diff([]string{"ctrl+c"}, ka.Normalized_keys); diff != "" {
+		t.Fatalf("Keys mismatch:\n%s", diff)
+	}
+
+	// Test space form: --allow-fallback shifted,ascii
+	ka, err = ParseMap("--allow-fallback shifted,ascii cmd+c copy_to_clipboard")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if ka.AllowFallback != "shifted,ascii" {
+		t.Fatalf("Expected AllowFallback 'shifted,ascii', got %#v", ka.AllowFallback)
+	}
+	if ka.Name != "copy_to_clipboard" {
+		t.Fatalf("Expected Name 'copy_to_clipboard', got %#v", ka.Name)
+	}
+
+	// Test --allow-fallback=none (equals form)
+	ka, err = ParseMap("--allow-fallback=none ctrl+c copy_to_clipboard")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if ka.AllowFallback != "" {
+		t.Fatalf("Expected AllowFallback '', got %#v", ka.AllowFallback)
+	}
+	if ka.Name != "copy_to_clipboard" {
+		t.Fatalf("Expected Name 'copy_to_clipboard', got %#v", ka.Name)
+	}
+
+	// Test --allow-fallback none (space form)
+	ka, err = ParseMap("--allow-fallback none ctrl+c copy_to_clipboard")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if ka.AllowFallback != "" {
+		t.Fatalf("Expected AllowFallback '', got %#v", ka.AllowFallback)
+	}
+	if ka.Name != "copy_to_clipboard" {
+		t.Fatalf("Expected Name 'copy_to_clipboard', got %#v", ka.Name)
+	}
+
+	// Test error: unknown flag
+	_, err = ParseMap("--allow-fallbak=ascii ctrl+c copy")
+	if err == nil {
+		t.Fatal("Expected error for unknown flag --allow-fallbak")
+	}
+
+	// Test error: unknown flag without =
+	_, err = ParseMap("--unknown ctrl+c copy")
+	if err == nil {
+		t.Fatal("Expected error for unknown flag --unknown")
+	}
+
+	// Test error: invalid allow-fallback value
+	_, err = ParseMap("--allow-fallback=typo ctrl+c copy")
+	if err == nil {
+		t.Fatal("Expected error for invalid allow-fallback value 'typo'")
+	}
+
+	// Test error: invalid allow-fallback value in space form
+	_, err = ParseMap("--allow-fallback typo ctrl+c copy")
+	if err == nil {
+		t.Fatal("Expected error for invalid allow-fallback value 'typo' in space form")
+	}
+}
+
 func TestNormalizeShortcuts(t *testing.T) {
 	for q, expected_ := range map[string]string{
 		`a`:           `a`,