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.test.ts

@@ -12,7 +12,10 @@ describe('validDisplayName', () => {
     ['Name P._Last', false],
     ['Name  Last', false],
     ['_Name', false],
-    ['Name.', false],
+    ['Anna B.', true],
+    ['Name.', true],
+    ['Name..', false],
+    ['Name_', false],
     ['Name2', false],
     ['', false],
     ['a'.repeat(33), false],