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).

docs/FUNCTIONAL.md

@@ -264,3 +264,27 @@ in-app), archive it, delete it, or delete every message from that player — and
 stops only feedback submission). Roles are listed and granted/revoked on the user card. Opening a
 message does not mark it read — only the explicit actions do; message bodies and attachments are
 shown defensively (text escaped, attachments downloaded rather than rendered).
+
+### Advertising banner
+
+A one-line banner under the nav shows short promotional or operational messages to **free
+players**: anyone who has **not** paid for a lifetime account, holds **no purchased hints**, and
+does not carry the **`no_banner`** role (which suppresses it unconditionally). Buying a paid account
+or any hints — or being granted `no_banner` — removes it; guests, the freest users, see it. When an
+operator changes one of those properties, the banner appears or disappears **in place**, without a
+reload.
+
+Messages come from operator-run **campaigns**, each a placement order with a **show weight** (a
+percent) and an optional start/end **window**. Campaigns running at the same time **compete** for the
+banner in proportion to their weights; a permanent **house (default)** campaign fills whatever share
+paid campaigns leave unsold and steps aside entirely when they sell the full 100%. Each message is
+written in **both languages** (English + Russian); a player sees the variant for the **bot they play
+through**, regardless of their interface language. The client rotates the eligible campaigns
+**fairly** — every campaign gets its weighted share each cycle, evenly spread rather than at random —
+and a campaign with several messages shows them in turn.
+
+Operators manage all of this in the admin console at **`/_gm/banners`**: create, edit, enable/disable
+and schedule campaigns, write each campaign's bilingual messages (reorder or remove them), and set
+the global display **timings** (how long a message holds, the scroll of an over-long message, and the
+fade-out → gap → fade-in transition between messages). The default campaign cannot be deleted and
+keeps at least one message.