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_repo.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"time"
 
+	"github.com/geo-platform/tenant-api/internal/tenant/prompts"
 	"github.com/geo-platform/tenant-api/internal/tenant/repository/generated"
 )
 
@@ -60,6 +61,7 @@ func (r *templateRepository) ListTemplates(ctx context.Context, tenantID int64)
 			CreatedAt:        timeFromTimestamp(row.CreatedAt),
 			UpdatedAt:        timeFromTimestamp(row.UpdatedAt),
 		})
+		applyPlatformTemplatePromptOverrides(&templates[len(templates)-1])
 	}
 
 	return templates, nil
@@ -74,7 +76,7 @@ func (r *templateRepository) GetTemplateByID(ctx context.Context, id, tenantID i
 		return nil, err
 	}
 
-	return &TemplateRecord{
+	record := &TemplateRecord{
 		ID:                      row.ID,
 		Scope:                   row.Scope,
 		TenantID:                nullableInt64(row.TenantID),
@@ -89,5 +91,18 @@ func (r *templateRepository) GetTemplateByID(ctx context.Context, id, tenantID i
 		VersionNo:               int(row.VersionNo),
 		CreatedAt:               timeFromTimestamp(row.CreatedAt),
 		UpdatedAt:               timeFromTimestamp(row.UpdatedAt),
-	}, nil
+	}
+	applyPlatformTemplatePromptOverrides(record)
+	return record, nil
+}
+
+func applyPlatformTemplatePromptOverrides(record *TemplateRecord) {
+	if record == nil || record.Scope != "platform" {
+		return
+	}
+	record.PromptTemplate, record.CardConfigJSON = prompts.ApplyPlatformTemplatePromptOverrides(
+		record.TemplateKey,
+		record.PromptTemplate,
+		record.CardConfigJSON,
+	)
 }