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/server/handlers_admin_console.go

@@ -88,6 +88,19 @@ func (s *Server) registerConsole(router *gin.Engine) {
 	gm.POST("/dictionary/changes/apply", s.consoleApplyChanges)
 	gm.GET("/broadcast", s.consoleBroadcast)
 	gm.POST("/broadcast", s.consolePostBroadcast)
+	if s.ads != nil {
+		gm.GET("/banners", s.consoleBanners)
+		gm.POST("/banners", s.consoleCreateBanner)
+		gm.GET("/banners/:id", s.consoleBannerDetail)
+		gm.POST("/banners/:id", s.consoleUpdateBanner)
+		gm.POST("/banners/:id/delete", s.consoleDeleteBanner)
+		gm.POST("/banners/:id/messages", s.consoleAddBannerMessage)
+		gm.POST("/banners/:id/messages/:mid", s.consoleEditBannerMessage)
+		gm.POST("/banners/:id/messages/:mid/delete", s.consoleDeleteBannerMessage)
+		gm.POST("/banners/:id/messages/:mid/move", s.consoleMoveBannerMessage)
+		gm.GET("/banner-settings", s.consoleBannerSettings)
+		gm.POST("/banner-settings", s.consoleUpdateBannerSettings)
+	}
 }
 
 // consoleDashboard renders the landing page: the top-line counts and the resident
@@ -817,6 +830,8 @@ func (s *Server) consoleGrantHints(c *gin.Context) {
 		s.consoleError(c, err)
 		return
 	}
+	// A non-empty hint wallet removes the banner: nudge an open client to re-check.
+	s.publishBannerChange(id)
 	s.renderConsoleMessage(c, "Granted", fmt.Sprintf("added %d hint(s); the wallet is now %d", n, balance), back)
 }