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

ui/src/lib/profileValidation.ts

@@ -9,9 +9,10 @@ export const maxDisplayName = 32;
 export const maxAwayMinutes = 12 * 60;
 
 // Unicode letters joined by single space / "." / "_" separators, where a "." or "_"
-// may be followed by a single space. No leading/trailing separator and no adjacent
-// separators except "<dot|underscore> <space>". Same rule as the Go displayNameRe.
-const displayNameRe = /^\p{L}+(?:(?:[._] ?| )\p{L}+)*$/u;
+// may be followed by a single space. No leading separator and no adjacent separators
+// except "<dot|underscore> <space>"; a single trailing "." is allowed (Stage 17). Same
+// rule as the Go displayNameRe.
+const displayNameRe = /^\p{L}+(?:(?:[._] ?| )\p{L}+)*\.?$/u;
 
 /** displayNameError returns true when the trimmed name is a valid display name. */
 export function validDisplayName(raw: string): boolean {