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).

ui/src/gen/fbs/scrabblefb/banner-campaign.ts

@@ -37,8 +37,50 @@ messagesLength():number {
   return offset ? this.bb!.__vector_len(this.bb_pos + offset) : 0;
 }
 
+overrideBg():string|null
+overrideBg(optionalEncoding:flatbuffers.Encoding):string|Uint8Array|null
+overrideBg(optionalEncoding?:any):string|Uint8Array|null {
+  const offset = this.bb!.__offset(this.bb_pos, 8);
+  return offset ? this.bb!.__string(this.bb_pos + offset, optionalEncoding) : null;
+}
+
+overrideFg():string|null
+overrideFg(optionalEncoding:flatbuffers.Encoding):string|Uint8Array|null
+overrideFg(optionalEncoding?:any):string|Uint8Array|null {
+  const offset = this.bb!.__offset(this.bb_pos, 10);
+  return offset ? this.bb!.__string(this.bb_pos + offset, optionalEncoding) : null;
+}
+
+overrideLink():string|null
+overrideLink(optionalEncoding:flatbuffers.Encoding):string|Uint8Array|null
+overrideLink(optionalEncoding?:any):string|Uint8Array|null {
+  const offset = this.bb!.__offset(this.bb_pos, 12);
+  return offset ? this.bb!.__string(this.bb_pos + offset, optionalEncoding) : null;
+}
+
+overrideBgDark():string|null
+overrideBgDark(optionalEncoding:flatbuffers.Encoding):string|Uint8Array|null
+overrideBgDark(optionalEncoding?:any):string|Uint8Array|null {
+  const offset = this.bb!.__offset(this.bb_pos, 14);
+  return offset ? this.bb!.__string(this.bb_pos + offset, optionalEncoding) : null;
+}
+
+overrideFgDark():string|null
+overrideFgDark(optionalEncoding:flatbuffers.Encoding):string|Uint8Array|null
+overrideFgDark(optionalEncoding?:any):string|Uint8Array|null {
+  const offset = this.bb!.__offset(this.bb_pos, 16);
+  return offset ? this.bb!.__string(this.bb_pos + offset, optionalEncoding) : null;
+}
+
+overrideLinkDark():string|null
+overrideLinkDark(optionalEncoding:flatbuffers.Encoding):string|Uint8Array|null
+overrideLinkDark(optionalEncoding?:any):string|Uint8Array|null {
+  const offset = this.bb!.__offset(this.bb_pos, 18);
+  return offset ? this.bb!.__string(this.bb_pos + offset, optionalEncoding) : null;
+}
+
 static startBannerCampaign(builder:flatbuffers.Builder) {
-  builder.startObject(2);
+  builder.startObject(8);
 }
 
 static addWeight(builder:flatbuffers.Builder, weight:number) {
@@ -61,15 +103,45 @@ static startMessagesVector(builder:flatbuffers.Builder, numElems:number) {
   builder.startVector(4, numElems, 4);
 }
 
+static addOverrideBg(builder:flatbuffers.Builder, overrideBgOffset:flatbuffers.Offset) {
+  builder.addFieldOffset(2, overrideBgOffset, 0);
+}
+
+static addOverrideFg(builder:flatbuffers.Builder, overrideFgOffset:flatbuffers.Offset) {
+  builder.addFieldOffset(3, overrideFgOffset, 0);
+}
+
+static addOverrideLink(builder:flatbuffers.Builder, overrideLinkOffset:flatbuffers.Offset) {
+  builder.addFieldOffset(4, overrideLinkOffset, 0);
+}
+
+static addOverrideBgDark(builder:flatbuffers.Builder, overrideBgDarkOffset:flatbuffers.Offset) {
+  builder.addFieldOffset(5, overrideBgDarkOffset, 0);
+}
+
+static addOverrideFgDark(builder:flatbuffers.Builder, overrideFgDarkOffset:flatbuffers.Offset) {
+  builder.addFieldOffset(6, overrideFgDarkOffset, 0);
+}
+
+static addOverrideLinkDark(builder:flatbuffers.Builder, overrideLinkDarkOffset:flatbuffers.Offset) {
+  builder.addFieldOffset(7, overrideLinkDarkOffset, 0);
+}
+
 static endBannerCampaign(builder:flatbuffers.Builder):flatbuffers.Offset {
   const offset = builder.endObject();
   return offset;
 }
 
-static createBannerCampaign(builder:flatbuffers.Builder, weight:number, messagesOffset:flatbuffers.Offset):flatbuffers.Offset {
+static createBannerCampaign(builder:flatbuffers.Builder, weight:number, messagesOffset:flatbuffers.Offset, overrideBgOffset:flatbuffers.Offset, overrideFgOffset:flatbuffers.Offset, overrideLinkOffset:flatbuffers.Offset, overrideBgDarkOffset:flatbuffers.Offset, overrideFgDarkOffset:flatbuffers.Offset, overrideLinkDarkOffset:flatbuffers.Offset):flatbuffers.Offset {
   BannerCampaign.startBannerCampaign(builder);
   BannerCampaign.addWeight(builder, weight);
   BannerCampaign.addMessages(builder, messagesOffset);
+  BannerCampaign.addOverrideBg(builder, overrideBgOffset);
+  BannerCampaign.addOverrideFg(builder, overrideFgOffset);
+  BannerCampaign.addOverrideLink(builder, overrideLinkOffset);
+  BannerCampaign.addOverrideBgDark(builder, overrideBgDarkOffset);
+  BannerCampaign.addOverrideFgDark(builder, overrideFgDarkOffset);
+  BannerCampaign.addOverrideLinkDark(builder, overrideLinkDarkOffset);
   return BannerCampaign.endBannerCampaign(builder);
 }
 }