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).

backend/internal/adminconsole/views.go

@@ -372,6 +372,58 @@ type MessageView struct {
 	Back    string
 }
 
+// BannersView is the advertising-campaign list page.
+type BannersView struct {
+	Items []BannerCampaignRow
+}
+
+// BannerCampaignRow is one campaign in the list. Window is a human-readable
+// validity window ("perpetual" for the default); ActiveNow reports whether it
+// would rotate right now (enabled and within its window).
+type BannerCampaignRow struct {
+	ID        string
+	Name      string
+	Weight    int
+	IsDefault bool
+	Enabled   bool
+	Window    string
+	Messages  int
+	ActiveNow bool
+}
+
+// BannerDetailView is the campaign detail/edit page. StartsAt/EndsAt are the
+// "YYYY-MM-DDTHH:MM" (UTC) values for the datetime-local inputs, empty when open.
+type BannerDetailView struct {
+	ID        string
+	Name      string
+	Weight    int
+	IsDefault bool
+	Enabled   bool
+	StartsAt  string
+	EndsAt    string
+	Messages  []BannerMessageRow
+}
+
+// BannerMessageRow is one bilingual message of a campaign. First/Last drive the
+// reorder buttons (disabled at the ends).
+type BannerMessageRow struct {
+	ID     string
+	BodyEn string
+	BodyRu string
+	First  bool
+	Last   bool
+}
+
+// BannerSettingsView is the global display-timings form.
+type BannerSettingsView struct {
+	HoldMs         int
+	EdgePauseMs    int
+	ScrollPxPerSec int
+	FadeOutMs      int
+	GapMs          int
+	FadeInMs       int
+}
+
 // FeedbackView is the paginated user-feedback queue. Status is the active
 // unread/read/archived filter; NameMask/ExtMask are the sender glob filters;
 // UserID pins the list to one account (the per-user link from /users);