feat: 添加分类提案功能，包括提案表单和相关后端逻辑

backend/src/main/resources/application.properties

@@ -13,6 +13,7 @@ spring.jpa.hibernate.ddl-auto=update
 spring.data.redis.host=${REDIS_HOST:localhost}
 spring.data.redis.port=${REDIS_PORT:6379}
 spring.data.redis.database=${REDIS_DATABASE:0}
+spring.data.redis.password=${REDIS_PASS: null}
 
 # for jwt
 app.jwt.secret=${JWT_SECRET:jwt_sec}

backend/src/main/resources/db/migration/V6__add_category_proposal_posts.sql

@@ -0,0 +1,25 @@
+-- Create table for category proposal posts (subclass of poll_posts)
+CREATE TABLE IF NOT EXISTS category_proposal_posts (
+    post_id BIGINT NOT NULL,
+    status VARCHAR(50) NOT NULL,
+    proposed_name VARCHAR(255) NOT NULL,
+    proposed_slug VARCHAR(255) NOT NULL,
+    description VARCHAR(255),
+    approve_threshold INT NOT NULL DEFAULT 60,
+    quorum INT NOT NULL DEFAULT 10,
+    start_at DATETIME(6) NULL,
+    result_snapshot LONGTEXT NULL,
+    reject_reason VARCHAR(255),
+    PRIMARY KEY (post_id),
+    CONSTRAINT fk_category_proposal_posts_parent
+        FOREIGN KEY (post_id) REFERENCES poll_posts (post_id)
+);
+
+CREATE INDEX IF NOT EXISTS idx_category_proposal_posts_status
+    ON category_proposal_posts (status);
+
+CREATE UNIQUE INDEX IF NOT EXISTS idx_category_proposal_posts_slug
+    ON category_proposal_posts (proposed_slug);
+
+
+