feat(prompts): add prompts loader and configuration management

- Implemented a new prompts loader in `loader.go` to manage prompt templates and configurations.
- Introduced caching mechanism for prompt configurations to optimize loading.
- Added functions to apply platform-specific prompt template overrides.
- Created unit tests in `loader_test.go` to validate prompt configuration loading and reloading behavior.
- Ensured that the last valid configuration is retained in case of errors during reload.

server/internal/tenant/repository/template_cache_repo.go

@@ -26,6 +26,9 @@ func (r *cachedTemplateRepository) ListTemplates(ctx context.Context, tenantID i
 	if data, err := r.cache.Get(ctx, key); err == nil {
 		var records []TemplateRecord
 		if err := json.Unmarshal(data, &records); err == nil {
+			for i := range records {
+				applyPlatformTemplatePromptOverrides(&records[i])
+			}
 			return records, nil
 		}
 	}
@@ -38,6 +41,9 @@ func (r *cachedTemplateRepository) ListTemplates(ctx context.Context, tenantID i
 	if data, err := json.Marshal(records); err == nil {
 		_ = r.cache.Set(ctx, key, data, templateCacheTTL)
 	}
+	for i := range records {
+		applyPlatformTemplatePromptOverrides(&records[i])
+	}
 	return records, nil
 }
 
@@ -47,6 +53,7 @@ func (r *cachedTemplateRepository) GetTemplateByID(ctx context.Context, id, tena
 	if data, err := r.cache.Get(ctx, key); err == nil {
 		var record TemplateRecord
 		if err := json.Unmarshal(data, &record); err == nil {
+			applyPlatformTemplatePromptOverrides(&record)
 			return &record, nil
 		}
 	}
@@ -59,5 +66,6 @@ func (r *cachedTemplateRepository) GetTemplateByID(ctx context.Context, id, tena
 	if data, err := json.Marshal(record); err == nil {
 		_ = r.cache.Set(ctx, key, data, templateCacheTTL)
 	}
+	applyPlatformTemplatePromptOverrides(record)
 	return record, nil
 }