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.

docs/FUNCTIONAL.md

@@ -146,8 +146,10 @@ yet holds to the plan once the bag empties, and plays at a human pace — short
 times for most moves, the occasional long one, and a night-time pause that tracks the
 player's own day. It answers a nudge
 within a few minutes and nudges back when the player has been away a long time. It
-carries a human-like, language-appropriate name (a Russian game draws mostly Russian
-names); it does not chat, and **silently ignores friend requests** — a request to a
+carries a human-like, language-appropriate name — a fresh one each game, drawn from a wide
+international pool of real names and handles, so the arena feels populated by many different
+players (a Russian game shows mostly Russian names, never East-Asian scripts; an international
+game the full mix); it does not chat, and **silently ignores friend requests** — a request to a
 robot stays pending and expires, exactly like a human who never responds.
 
 The same robot also backs the **honest-AI quick game** the player chooses directly (above). There
@@ -182,8 +184,9 @@ message raises an **unread badge** on the game's score bar and the 💬 until th
 
 ### Profile & settings
 Edit the display name (letters joined by a single space / "." / "_" separator, with an
-optional trailing ".", up to 32 characters and at most 5 special characters — the "." / "_"
-punctuation, spaces aside), the timezone (chosen as a UTC offset), the
+optional trailing "." or a trailing run of up to five digits, up to 32 characters and at most
+5 special characters — the "." / "_" punctuation, spaces and digits aside), the timezone
+(chosen as a UTC offset), the
 daily away window (on a 10-minute grid, at most 12 hours, wrapping midnight) and the
 block toggles. The profile form is edited inline (no separate edit mode). Linking
 an email or Telegram and merging accounts are covered under "Accounts, linking &