feat(robot): per-game display names from a wide name corpus

Decouple the displayed opponent name from the small pool of durable robot
accounts: the disguised auto-match robot now gets a freshly composed name each
game, stamped on a new game_players.display_name seat snapshot. The snapshot
also captures humans' names, freezing what an opponent sees for the life of a
game (a later rename no longer rewrites past games); readers fall back to the
account's current name for pre-migration rows.

Names come from a wide composed corpus (internal/robot/namevariety.go): Western
locales (EN/DE/ES/IT/FR/PT), native Japanese/Chinese names, a gender-agreed
Russian pool, and human-style handles. Routing keeps Pick's spirit -- a Russian
game draws Cyrillic + <=20% Latin and never a CJK script; an English game the
full corpus -- via robot.PickNamed.

Loosen account.ValidateDisplayName (and the UI mirror) to admit a trailing run
of up to five digits, so "Player2007"-style handles are valid for humans too
and the disguised robot stays indistinguishable.

Migration 00007 adds game_players.display_name (additive, NOT NULL DEFAULT '');
jet regenerated. Docs (ARCHITECTURE 7, FUNCTIONAL + _ru, PLAN, README) updated.

ui/src/lib/profileValidation.test.ts

@@ -16,7 +16,16 @@ describe('validDisplayName', () => {
     ['Name.', true],
     ['Name..', false],
     ['Name_', false],
-    ['Name2', false],
+    ['Name2', true], // a trailing digit is allowed
+    ['Аня2007', true], // a trailing year
+    ['Player12345', true], // 5 trailing digits — the max
+    ['Player123456', false], // 6 trailing digits — over the limit
+    ['Dark2Wolf', false], // a digit in the middle
+    ['12345', false], // must start with a letter
+    ['Name2.', false], // digits and a trailing dot cannot combine
+    ['Anna B.2', false], // a trailing dot and digits cannot combine
+    ['Night.Fox2007', true], // one "." special; digits do not count
+    ['a.a.a.a.a.a2007', true], // 5 dots + a digit run still passes
     ['', false],
     ['a'.repeat(33), false],
     ['a.a.a.a.a.a', true], // 5 dots — at the special-char limit