refactor(#300 ui): extract avatar palette into generated OKLCH module

Replace the inline hand-transcribed palette with the self-contained
src/lib/avatar-palette.ts: the 20-color palette is GENERATED at module load
from an OKLCH ring config (chroma clamped to sRGB, WCAG text color per color),
so it is fully tunable and validated (min pairwise ΔE-OK ≈ 0.066).

avatarStyle() slices one cyrb53 hash of the normalized name into independent
channels: base color (20) × color-wheel scheme (analogous ±20–45° / complement
180° / triadic ±120°) × split angle (24 dirs). avatarBackgroundCss() renders a
two-stop gradient with a soft boundary. Pure, cross-platform, deterministic —
same name → same avatar everywhere, nothing persisted.

The glyph now consumes avatarStyle/avatarBackgroundCss from the module;
agent-avatar-stack no longer defines its own hash/palette.

Tests: avatar-palette.test.ts pins minPairwiseDistance ≥ 0.06, PALETTE length,
normalization, and a golden name→style slice (Backend Developer →
#a55795/#90355e/150°) so a config change that repaints every avatar can't slip
through unnoticed. client tsc clean, 30 tests pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/client/src/components/ui/agent-avatar-stack.tsx

@@ -4,6 +4,7 @@ import { useCallback } from "react";
 import { useTranslation } from "react-i18next";
 import { useSetAtom } from "jotai";
 import { CustomAvatar } from "@/components/ui/custom-avatar.tsx";
+import { avatarStyle, avatarBackgroundCss } from "@/lib/avatar-palette";
 import {
   activeAiChatIdAtom,
   aiChatWindowOpenAtom,
@@ -29,91 +30,6 @@ const LAUNCHER_SIZE = 22;
 // sits as a small badge over that corner (above the glyph) and stays fully visible.
 const LAUNCHER_OVERHANG = 8;
 
-// Normalize the name before hashing so "PM ", "pm", "Pm" all map to the same
-// avatar (unicode-normalized, trimmed, lower-cased, whitespace collapsed).
-function normalizeName(name: string): string {
-  return name.normalize("NFC").trim().toLowerCase().replace(/\s+/g, " ");
-}
-
-// cyrb53: deterministic 53-bit string hash with good avalanche, pure JS. A
-// language's BUILT-IN hash (Java hashCode, etc.) must NOT be used — those differ
-// across platforms/engines, which would make one name render as different avatars
-// on server vs client. This is stable everywhere.
-function cyrb53(str: string, seed = 0): number {
-  let h1 = 0xdeadbeef ^ seed;
-  let h2 = 0x41c6ce57 ^ seed;
-  for (let i = 0; i < str.length; i += 1) {
-    const ch = str.charCodeAt(i);
-    h1 = Math.imul(h1 ^ ch, 2654435761);
-    h2 = Math.imul(h2 ^ ch, 1597334677);
-  }
-  h1 =
-    Math.imul(h1 ^ (h1 >>> 16), 2246822507) ^
-    Math.imul(h2 ^ (h2 >>> 13), 3266489909);
-  h2 =
-    Math.imul(h2 ^ (h2 >>> 16), 2246822507) ^
-    Math.imul(h1 ^ (h1 >>> 13), 3266489909);
-  return 4294967296 * (2097151 & h2) + (h1 >>> 0);
-}
-
-// Perceptually-even avatar palette built in OKLCH and clamped to the sRGB gamut:
-// 12 LIGHT colors (L≈0.70, black text) then 8 DARK colors (L≈0.50, white text).
-// The minimum pairwise ΔEOK ≈ 0.066 (~5 JNDs), so any two entries are either the
-// SAME color or clearly distinguishable — "almost identical" colors are
-// impossible by construction (that was the old raw-hue failure mode). Text
-// contrast is WCAG-checked: dark ring ≥ 5.6:1 white, light ring ≥ 7.3:1 black.
-export const AVATAR_PALETTE = [
-  // light ring (black text)
-  "#e87782", "#e57f4f", "#d0901e", "#aca220", "#77b154", "#22b988",
-  "#00b5b5", "#00afdc", "#5fa1f3", "#9690f1", "#bf82da", "#db78b2",
-  // dark ring (white text)
-  "#a03e43", "#8e5300", "#686800", "#007742",
-  "#007176", "#0068a5", "#6453a7", "#8f4280",
-];
-
-// Second gradient stop per palette entry (index-aligned): two hue-shifted (±25°)
-// partners. A separate hash channel picks which one, so two agents that collide
-// on the base color almost always still differ by their gradient.
-export const GRADIENT_PARTNERS = [
-  ["#de77ab", "#e67d58"], ["#e8777a", "#d58d25"], ["#e28247", "#b39f18"],
-  ["#cb9317", "#81af4b"], ["#a4a528", "#37b880"], ["#6cb35d", "#00b6af"],
-  ["#3cb693", "#26afd1"], ["#00b4bb", "#58a3ed"], ["#00ade4", "#8e93f3"],
-  ["#699ef5", "#b984df"], ["#9e8eef", "#d779ba"], ["#c480d4", "#e7768a"],
-  ["#9a3e67", "#9d4616"], ["#974a2e", "#7a6000"], ["#7e5e00", "#47712c"],
-  ["#4b7015", "#007465"], ["#1c7360", "#1c6d88"], ["#006f87", "#485daa"],
-  ["#3e5fad", "#7f4995"], ["#7a4b9a", "#9c3e60"],
-];
-
-export interface AvatarStyle {
-  bg: string; // base color / first gradient stop
-  bg2: string; // second gradient stop
-  angleDeg: number; // gradient direction
-  text: "white" | "black"; // readable foreground for the ring
-}
-
-/**
- * Deterministic, cross-platform avatar style for an agent glyph. Disjoint bit
- * ranges of ONE cyrb53 hash drive INDEPENDENT visual channels — palette color
- * (20) × gradient partner (2) × gradient angle (8) = 320 combinations — so even
- * when the base color repeats (unavoidable: humans reliably tell apart only
- * ~20-25 colors), the gradient — and the emoji drawn on top — still tell two
- * agents apart. Pure function of the normalized name: same name → same avatar on
- * every device, nothing persisted.
- */
-export function avatarStyle(agentName: string): AvatarStyle {
-  const h = cyrb53(normalizeName(agentName));
-  const idx = h % AVATAR_PALETTE.length; // which palette color
-  const rest = Math.floor(h / AVATAR_PALETTE.length);
-  const dir = rest % 2; // gradient partner: hue -25 or +25
-  const angleDeg = (Math.floor(rest / 2) % 8) * 45; // one of 8 gradient angles
-  return {
-    bg: AVATAR_PALETTE[idx],
-    bg2: GRADIENT_PARTNERS[idx][dir],
-    angleDeg,
-    text: idx < 12 ? "black" : "white",
-  };
-}
-
 /**
  * The front avatar. Image-source priority (#300):
  *   1. agent.avatarUrl -> a real avatar image (external MCP agent account).
@@ -131,8 +47,9 @@ function AgentGlyph({ agent }: { agent: AgentInfo }) {
     );
   }
 
-  // Emoji/sparkles glyph on a per-agent gradient circle (color + gradient hashed
-  // from the agent name via avatarStyle). Rendered as a plain Box, NOT a Mantine
+  // Emoji/sparkles glyph on a per-agent gradient circle (color, gradient partner
+  // and split angle all hashed from the agent name via avatarStyle — see
+  // @/lib/avatar-palette). Rendered as a plain Box, NOT a Mantine
   // `Avatar variant="filled"` — Mantine's `--avatar-bg` overrode the background
   // (every agent fell back to the theme's violet). The foreground (the sparkles
   // icon) uses the ring's WCAG-checked readable text color.
@@ -147,7 +64,7 @@ function AgentGlyph({ agent }: { agent: AgentInfo }) {
         // Solid base color is the fallback (and the testable value); the gradient
         // paints over it in browsers that support it.
         backgroundColor: style.bg,
-        backgroundImage: `linear-gradient(${style.angleDeg}deg, ${style.bg}, ${style.bg2})`,
+        backgroundImage: avatarBackgroundCss(style),
         color:
           style.text === "white"
             ? "var(--mantine-color-white)"