feat: 新增标签分类体系与固定类型筛选优化

prisma/schema.prisma

@@ -88,9 +88,11 @@ model Tag {
   name         String         @unique
   nameEn       String?
   slug         String         @unique
+  category     TagCategory    @default(FREE_TAG)
   createdAt    DateTime       @default(now())
   projects     ProjectTag[]
 
+  @@index([category], map: "idx_tag_category")
   @@index([slug], map: "idx_tag_slug")
   @@map("tags")
 }
@@ -114,3 +116,13 @@ enum TaskStatus {
   FAILED
 }
 
+enum TagCategory {
+  FIXED_PROJECT_TYPE
+  TECH_STACK
+  AI_PARADIGM
+  PROTOCOL_INTERFACE
+  PRODUCT_FORM
+  DOMAIN_SCENARIO
+  RESOURCE_TYPE
+  FREE_TAG
+}