fix(cli): restore model.prompt-based system prompt selection

The switch(model.prompt) block in SystemPrompt.provider() was
accidentally dropped during merge conflict resolution in fa2c979ac.
This meant the prompt property set by the Kilo gateway (e.g. codex,
anthropic, beast) was stored on the model but never read, causing all
Kilo-routed models to fall back to model.api.id string matching.

packages/opencode/src/session/system.ts

@@ -34,6 +34,23 @@ export namespace SystemPrompt {
   // kilocode_change end
 
   export function provider(model: Provider.Model) {
+    // kilocode_change start
+    switch (model.prompt) {
+      case "anthropic":
+        return [PROMPT_ANTHROPIC]
+      case "anthropic_without_todo":
+        return [PROMPT_DEFAULT]
+      case "beast":
+        return [PROMPT_BEAST]
+      case "codex":
+        return [PROMPT_CODEX]
+      case "gemini":
+        return [PROMPT_GEMINI]
+      case "trinity":
+        return [PROMPT_TRINITY]
+    }
+    // kilocode_change end
+
     if (model.api.id.includes("gpt-4") || model.api.id.includes("o1") || model.api.id.includes("o3"))
       return [PROMPT_BEAST]
     if (model.api.id.includes("gpt")) {