style(agents): update Hephaestus and Prometheus colors

- Hephaestus: #FF4500 (Magma Orange) → #708090 (Slate Gray)
  Blacksmith's hammer/iron theme, visible in both light and dark modes

- Prometheus: #9D4EDD (Amethyst Purple) → #FF5722 (Deep Orange)
  Fire/flame theme, restoring the original fire color concept

src/plugin-handlers/config-handler.ts

@@ -305,7 +305,7 @@ export function createConfigHandler(deps: ConfigHandlerDeps) {
           prompt: PROMETHEUS_SYSTEM_PROMPT,
           permission: PROMETHEUS_PERMISSION,
           description: `${configAgent?.plan?.description ?? "Plan agent"} (Prometheus - OhMyOpenCode)`,
-          color: (configAgent?.plan?.color as string) ?? "#9D4EDD", // Amethyst Purple - wisdom/foresight
+          color: (configAgent?.plan?.color as string) ?? "#FF5722", // Deep Orange - Fire/Flame theme
           ...(temperatureToUse !== undefined ? { temperature: temperatureToUse } : {}),
           ...(topPToUse !== undefined ? { top_p: topPToUse } : {}),
           ...(maxTokensToUse !== undefined ? { maxTokens: maxTokensToUse } : {}),