Stage 17: fix the robot-nudge frequency + per-game push language

Two owner-reported defects from a live contour game.

A. Frequency: the robot's proactive nudge fired hourly for 12h+ (a 12h idle threshold
   then the 1h cooldown, uncapped). Replaced with a lengthening, randomized schedule
   (proactiveNudgeGap): the first nudge ~60-90 min into the human's turn, each later gap
   growing toward 1-6h (uniform sample in [60min, ceil], ceil ramping 90min->6h over 12h
   of idle, measured from the previous nudge), so a long wait gets a handful of
   increasingly-spaced reminders instead of a stream.

B. Language: out-of-app push routed by the recipient's GLOBAL service_language
   (last-login-wins), so after re-logging via the RU bot an English game's nudges came
   from the RU bot. Now a game push (your_turn, game_over, nudge, match_found) carries
   the game's own language (engine.Variant.Language) on push.Event, and the gateway
   routes by it (falling back to service_language for non-game pushes). The New-Game
   variant-gating guarantees the game's bot is one the player has started, so delivery is
   never blocked.

Tests: proactiveNudgeGap unit + retimed TestRobotProactiveNudge; TestVariantLanguage;
emit your_turn/game_over language; TestNudgeRoutedByGameLanguage integration. Docs:
ARCHITECTURE (§7 nudge, §10/§13 routing), FUNCTIONAL (+ _ru), PLAN tracker.

PLAN.md

@@ -1461,6 +1461,20 @@ provided cert) at the contour caddy; prod VPN; rollback.
       game bar (commit/exchange/pass/hint/resign), chat send + nudge, profile save / link / merge,
       friends (request/respond/unfriend/block/code), New Game (auto-match + invite) and the lobby
       hide ❌; purely local controls (board/rack/reset, menu, navigation, settings) stay live.
+    - **Nudge defects (owner-reported, shipped):** two from a live contour game.
+      **(A) Frequency** — the robot's proactive nudge fired hourly for 12 h+ (12 h idle threshold +
+      the 1 h cooldown, uncapped). Replaced with a **lengthening, randomized schedule** in the
+      robot strategy/driver: the first nudge ~60-90 min into the human's turn, each later gap
+      growing toward 1-6 h (the gap is a uniform sample in `[60 min, ceil]`, `ceil` ramping from
+      90 min to 6 h over 12 h of idle, measured from the previous nudge), so a long wait gets a
+      handful of increasingly-spaced reminders. **(B) Language** — the out-of-app push routed by
+      the recipient's **global `service_language`** (last-login-wins), so after re-logging through
+      the RU bot an English game's nudges came from the RU bot. Now a game push (your_turn,
+      game_over, nudge, match_found) carries the **game's own language** (`engine.Variant.Language`)
+      on `push.Event`, and the gateway routes by it (falling back to `service_language` for
+      non-game pushes); the New-Game variant-gating guarantees deliverability. Covered by the
+      `proactiveNudgeGap` unit test, the retimed `TestRobotProactiveNudge`, `TestVariantLanguage`,
+      emit (`your_turn`/`game_over` language) and a `TestNudgeRoutedByGameLanguage` integration test.
 
 ## Deferred TODOs (cross-stage)