feat(banner): per-campaign colour overrides and urgent alerts

Non-default campaigns gain an optional colour override (background / text /
link) in two sets — one for every theme, one for the dark theme only — and an
"urgent" flag.

- Colours ride profile.get as six trailing FlatBuffers strings on
  BannerCampaign (backward-compatible). The client resolves the cascade
  (dark <- dark ?? all, light <- all) per rendered theme and derives the strip
  border from the background in JS (no CSS color-mix, for the old Android
  WebView floor); AdBanner applies them as inline vars scoped to the strip.
- Urgent is resolved entirely server-side: while any enabled, in-window urgent
  campaign exists, computeActiveSet returns only the urgent campaigns and
  bannerFor skips the eligibility gate — so a system notice reaches every viewer
  (paid / hint-holding / no_banner included) and preempts the ordinary feed. No
  wire field; it appears on each viewer's next profile.get.
- Admin console (/_gm/banners): native colour pickers + a live light/dark
  preview of the strip, and an urgent toggle. The default campaign stays plain,
  enforced by the service and a DB CHECK.

Migration 00009 is additive (nullable colour columns + a bool default +
all-or-nothing / hex / default-plain CHECKs) — expand-contract, rollback-safe.

Docs: ARCHITECTURE §10, UI_DESIGN, FUNCTIONAL (+ru). Tests: ads unit (urgent
preempt + colour validation), codec + resolver unit, gateway transcode, and
integration (colour round-trip + urgent bypass against real Postgres).

backend/internal/ads/store.go

@@ -90,15 +90,23 @@ func (s *Store) Campaign(ctx context.Context, id uuid.UUID) (Campaign, error) {
 func (s *Store) CreateCampaign(ctx context.Context, c Campaign) (uuid.UUID, error) {
 	id := uuid.New()
 	now := time.Now().UTC()
+	abg, afg, alink := colorCols(c.OverrideAll)
+	dbg, dfg, dlink := colorCols(c.OverrideDark)
 	stmt := table.AdCampaigns.INSERT(
 		table.AdCampaigns.CampaignID, table.AdCampaigns.Name, table.AdCampaigns.Weight,
 		table.AdCampaigns.IsDefault, table.AdCampaigns.Enabled,
 		table.AdCampaigns.StartsAt, table.AdCampaigns.EndsAt,
+		table.AdCampaigns.OverrideBg, table.AdCampaigns.OverrideFg, table.AdCampaigns.OverrideLink,
+		table.AdCampaigns.OverrideBgDark, table.AdCampaigns.OverrideFgDark, table.AdCampaigns.OverrideLinkDark,
+		table.AdCampaigns.Urgent,
 		table.AdCampaigns.CreatedAt, table.AdCampaigns.UpdatedAt,
 	).VALUES(
 		postgres.UUID(id), postgres.String(c.Name), postgres.Int(int64(c.Weight)),
 		postgres.Bool(false), postgres.Bool(c.Enabled),
 		tsOrNull(c.StartsAt), tsOrNull(c.EndsAt),
+		abg, afg, alink,
+		dbg, dfg, dlink,
+		postgres.Bool(c.Urgent),
 		postgres.TimestampzT(now), postgres.TimestampzT(now),
 	)
 	if _, err := stmt.ExecContext(ctx, s.db); err != nil {
@@ -111,12 +119,20 @@ func (s *Store) CreateCampaign(ctx context.Context, c Campaign) (uuid.UUID, erro
 // window. The default flag is never touched here. Returns ErrNotFound when no
 // campaign matches.
 func (s *Store) UpdateCampaign(ctx context.Context, c Campaign) error {
+	abg, afg, alink := colorCols(c.OverrideAll)
+	dbg, dfg, dlink := colorCols(c.OverrideDark)
 	stmt := table.AdCampaigns.UPDATE(
 		table.AdCampaigns.Name, table.AdCampaigns.Weight, table.AdCampaigns.Enabled,
-		table.AdCampaigns.StartsAt, table.AdCampaigns.EndsAt, table.AdCampaigns.UpdatedAt,
+		table.AdCampaigns.StartsAt, table.AdCampaigns.EndsAt,
+		table.AdCampaigns.OverrideBg, table.AdCampaigns.OverrideFg, table.AdCampaigns.OverrideLink,
+		table.AdCampaigns.OverrideBgDark, table.AdCampaigns.OverrideFgDark, table.AdCampaigns.OverrideLinkDark,
+		table.AdCampaigns.Urgent, table.AdCampaigns.UpdatedAt,
 	).SET(
 		postgres.String(c.Name), postgres.Int(int64(c.Weight)), postgres.Bool(c.Enabled),
-		tsOrNull(c.StartsAt), tsOrNull(c.EndsAt), postgres.TimestampzT(time.Now().UTC()),
+		tsOrNull(c.StartsAt), tsOrNull(c.EndsAt),
+		abg, afg, alink,
+		dbg, dfg, dlink,
+		postgres.Bool(c.Urgent), postgres.TimestampzT(time.Now().UTC()),
 	).WHERE(table.AdCampaigns.CampaignID.EQ(postgres.UUID(c.ID)))
 	return execOne(ctx, s.db, stmt, "update campaign")
 }
@@ -257,18 +273,40 @@ func execOne(ctx context.Context, db qrm.Executable, stmt postgres.Statement, wh
 
 func modelToCampaign(r model.AdCampaigns) Campaign {
 	return Campaign{
-		ID:        r.CampaignID,
-		Name:      r.Name,
-		Weight:    int(r.Weight),
-		IsDefault: r.IsDefault,
-		Enabled:   r.Enabled,
-		StartsAt:  r.StartsAt,
-		EndsAt:    r.EndsAt,
-		CreatedAt: r.CreatedAt,
-		UpdatedAt: r.UpdatedAt,
+		ID:           r.CampaignID,
+		Name:         r.Name,
+		Weight:       int(r.Weight),
+		IsDefault:    r.IsDefault,
+		Enabled:      r.Enabled,
+		StartsAt:     r.StartsAt,
+		EndsAt:       r.EndsAt,
+		OverrideAll:  colorSetFrom(r.OverrideBg, r.OverrideFg, r.OverrideLink),
+		OverrideDark: colorSetFrom(r.OverrideBgDark, r.OverrideFgDark, r.OverrideLinkDark),
+		Urgent:       r.Urgent,
+		CreatedAt:    r.CreatedAt,
+		UpdatedAt:    r.UpdatedAt,
 	}
 }
 
+// colorSetFrom rebuilds an optional ColorSet from three nullable colour columns.
+// The all-or-nothing CHECK keeps the trio consistent, so a nil in any one means
+// the set is absent.
+func colorSetFrom(bg, fg, link *string) *ColorSet {
+	if bg == nil || fg == nil || link == nil {
+		return nil
+	}
+	return &ColorSet{Bg: *bg, Fg: *fg, Link: *link}
+}
+
+// colorCols renders a *ColorSet as its three column value-expressions in
+// bg, fg, link order — NULL for each when the set is absent.
+func colorCols(cs *ColorSet) (bg, fg, link postgres.Expression) {
+	if cs == nil {
+		return postgres.NULL, postgres.NULL, postgres.NULL
+	}
+	return postgres.String(cs.Bg), postgres.String(cs.Fg), postgres.String(cs.Link)
+}
+
 func modelToMessage(r model.AdMessages) Message {
 	return Message{
 		ID:         r.MessageID,