fix(sql): remove foreign key constraints from forum tables

FK references to users table fail when users table doesn't exist yet.
Application layer ensures data consistency.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: yyyCode

sql/forum.sql

@@ -1,4 +1,5 @@
 -- 论坛话题表
+-- 注意：未加外键约束，因为目标库可能尚无 users 表，应用层保证数据一致性
 CREATE TABLE IF NOT EXISTS forum_topics (
     id BIGINT AUTO_INCREMENT PRIMARY KEY,
     title VARCHAR(200) NOT NULL,
@@ -10,8 +11,7 @@ CREATE TABLE IF NOT EXISTS forum_topics (
     created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
     updated_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
     INDEX idx_topics_status_created (status, created_at DESC),
-    INDEX idx_topics_author (author_id),
-    CONSTRAINT fk_forum_topics_author FOREIGN KEY (author_id) REFERENCES users(id)
+    INDEX idx_topics_author (author_id)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
 
 -- 论坛评论表
@@ -23,7 +23,5 @@ CREATE TABLE IF NOT EXISTS forum_comments (
     status VARCHAR(16) NOT NULL DEFAULT 'APPROVED' COMMENT 'APPROVED / DELETED',
     created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
     INDEX idx_comments_topic_created (topic_id, created_at ASC),
-    INDEX idx_comments_author (author_id),
-    CONSTRAINT fk_forum_comments_topic FOREIGN KEY (topic_id) REFERENCES forum_topics(id),
-    CONSTRAINT fk_forum_comments_author FOREIGN KEY (author_id) REFERENCES users(id)
+    INDEX idx_comments_author (author_id)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;