feat(ads): server-driven ad-banner backend, wire & admin console (PR1)

Turn the gated-off mock banner into a real advertising subsystem (backend +
admin half; the UI rotation lands in PR2).

- internal/ads: campaigns (percent weight + validity window; a perpetual,
  undeletable default that fills the remainder up to 100%), 1..N bilingual
  messages (en+ru), global display timings; ActiveSet computes the
  window-filtered, default-remainder, GCD-reduced, language-resolved rotation
  feed. Smooth-weighted-round-robin math is unit-tested.
- migration 00006 (+ jetgen): ad_campaigns / ad_messages / ad_settings, seeded
  default campaign + house message + default timings.
- eligibility = !paid_account && hint_balance==0 && !no_banner role (new role;
  guests qualify). The resolved feed rides the profile.get response (no new RPC,
  works for guests, nothing distinct to filter); language by service_language.
- live update: a notify `banner` sub-kind (re-poll signal) published when an
  operator grants hints or grants/revokes no_banner, so the client shows/hides
  in place.
- admin console /_gm/banners (+ /_gm/banner-settings): campaign + message CRUD
  with reorder, default protection, clamped timings.
- wire: fbs BannerInfo/BannerCampaign on Profile; gateway transcode forwards it.
- docs: ARCHITECTURE §10, FUNCTIONAL (+ _ru), backend README, PRERELEASE tracker
  (incl. the deferred app.load aggregator note).

pkg/fbs/scrabble.fbs

@@ -137,12 +137,39 @@ table Ack {
   ok:bool;
 }
 
+// --- advertising banner ---
+
+// BannerCampaign is one campaign in the rotation feed: a GCD-reduced show weight
+// (the client runs a smooth weighted round-robin over campaigns by this weight)
+// and its messages in display order, each already resolved to the viewer's bot
+// language (the stored en/ru pair is picked server-side).
+table BannerCampaign {
+  weight:int;
+  messages:[string];
+}
+
+// BannerInfo is the advertising-banner block of an eligible viewer's profile: the
+// campaigns to rotate and the global display timings the client rotator reads.
+// It is present (set on Profile.banner) only when the viewer is eligible to see a
+// banner; absent otherwise. The transition between messages is fade_out_ms, then
+// gap_ms, then fade_in_ms.
+table BannerInfo {
+  campaigns:[BannerCampaign];
+  hold_ms:int;
+  edge_pause_ms:int;
+  scroll_px_per_sec:int;
+  fade_out_ms:int;
+  gap_ms:int;
+  fade_in_ms:int;
+}
+
 // --- profile (authenticated) ---
 
 // Profile is the authenticated account's own profile view. away_start/away_end are
 // the "HH:MM" daily away-window bounds. notifications_in_app_only (default true)
-// suppresses out-of-app platform push, leaving only the in-app live stream (both
-// added trailing — backward-compatible).
+// suppresses out-of-app platform push, leaving only the in-app live stream. banner
+// carries the advertising-banner block for an eligible viewer, absent otherwise
+// (all added trailing — backward-compatible).
 table Profile {
   user_id:string;
   display_name:string;
@@ -155,6 +182,7 @@ table Profile {
   away_start:string;
   away_end:string;
   notifications_in_app_only:bool = true;
+  banner:BannerInfo;
 }
 
 // BlockStatus reports the caller's current manual block. The UI fetches it after any operation