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/profile.go

@@ -28,9 +28,10 @@ const maxAwayWindow = 12 * time.Hour
 
 // displayNameRe enforces the editable display-name format (Stage 8): Unicode letters
 // joined by single space / "." / "_" separators, where a "." or "_" may be followed
-// by a single space. No leading or trailing separator and no two adjacent separators,
-// except "<dot|underscore> <space>". So "Name_P. Last" is valid, "Name P._Last" is not.
-var displayNameRe = regexp.MustCompile(`^\p{L}+(?:(?:[._] ?| )\p{L}+)*$`)
+// by a single space. No leading separator and no two adjacent separators (except
+// "<dot|underscore> <space>"); a single trailing "." is allowed (Stage 17), so
+// "Name_P. Last" and "Anna B." are valid, "Name P._Last" is not.
+var displayNameRe = regexp.MustCompile(`^\p{L}+(?:(?:[._] ?| )\p{L}+)*\.?$`)
 
 // ErrInvalidProfile is returned when a profile update carries an unacceptable
 // field (an unknown language, an invalid timezone, or an over-long display name).