feat: switch to MiniCPM5-1B-Claude-Opus-Fable5-V2-Thinking-Q8_0 GGUF

- Updated model path + model ID for new 1B thinking model
- Updated prompt builder to use MiniCPM5 native /think trigger
- Updated clean_text to strip MiniCPM5 special tokens
- Bumped n_ctx from 2048 to 8192

src/presentation/handler/health.rs

@@ -8,6 +8,6 @@ use crate::domain::entity::HealthResponse;
 pub async fn health_check() -> Json<HealthResponse> {
     Json(HealthResponse {
         status: "ok".into(),
-        model: format!("{MODEL_ID}-q4_k_m"),
+        model: format!("{MODEL_ID}-q8_0"),
     })
 }