Stage 17 (contour round 4a): quick fixes

- #4 bag label: '{n} in the bag' / 'Bag is empty' (was 'Bag {n}')
- #6 allow a single trailing dot in display names (backend + UI regex + tests)
- #1 double-tap zooms toward the tapped cell, not the top-left
- #8 shuffle fires a short multi-pulse haptic
- #11 highlighted/flashing tiles darken their bottom edge too (shadow joins the flash)
- #13 toast slides up from the bottom and fades out
- #7 hide the logout button (kept wired behind `hidden`)
- #16 admin game seats: left-align numeric columns, clarify the 'Hints used' header

backend/internal/account/validate_test.go

@@ -12,19 +12,21 @@ func TestValidateDisplayName(t *testing.T) {
 		want string
 		ok   bool
 	}{
-		"plain":              {"Kaya", "Kaya", true},
-		"cyrillic":           {"Кая", "Кая", true},
-		"dot underscore mix": {"Name_P. Last", "Name_P. Last", true},
-		"single dot":         {"Mr.Smith", "Mr.Smith", true},
-		"dot then space":     {"Mr. Smith", "Mr. Smith", true},
-		"trim surrounding":   {"  Kaya  ", "Kaya", true},
-		"adjacent specials":  {"Name P._Last", "", false},
-		"two spaces":         {"Name  Last", "", false},
-		"leading special":    {"_Name", "", false},
-		"trailing special":   {"Name.", "", false},
-		"digit rejected":     {"Name2", "", false},
-		"blank":              {"   ", "", false},
-		"too long":           {strings.Repeat("a", 33), "", false},
+		"plain":               {"Kaya", "Kaya", true},
+		"cyrillic":            {"Кая", "Кая", true},
+		"dot underscore mix":  {"Name_P. Last", "Name_P. Last", true},
+		"single dot":          {"Mr.Smith", "Mr.Smith", true},
+		"dot then space":      {"Mr. Smith", "Mr. Smith", true},
+		"trim surrounding":    {"  Kaya  ", "Kaya", true},
+		"adjacent specials":   {"Name P._Last", "", false},
+		"two spaces":          {"Name  Last", "", false},
+		"leading special":     {"_Name", "", false},
+		"trailing underscore": {"Name_", "", false},
+		"trailing dot ok":     {"Anna B.", "Anna B.", true},
+		"double trailing dot": {"Name..", "", false},
+		"digit rejected":      {"Name2", "", false},
+		"blank":               {"   ", "", false},
+		"too long":            {strings.Repeat("a", 33), "", false},
 	}
 	for name, tc := range cases {
 		t.Run(name, func(t *testing.T) {