feat: implement chat and conversation history management with database schema and API endpoints

db/migrations/0000015_chat_and_support.up.sql

@@ -0,0 +1,34 @@
+CREATE TABLE IF NOT EXISTS conversations (
+    id UUID PRIMARY KEY DEFAULT uuidv7(),
+    user_id UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    mod_id UUID REFERENCES users(id) ON DELETE SET NULL,
+    status SMALLINT NOT NULL DEFAULT 1, -- 1: waiting, 2: active, 3: resolved
+    closed_at TIMESTAMPTZ,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX idx_conversations_user_id ON conversations (user_id);
+CREATE INDEX idx_conversations_mod_id ON conversations (mod_id);
+CREATE INDEX idx_conversations_status ON conversations (status);
+
+CREATE TABLE IF NOT EXISTS messages (
+    id UUID PRIMARY KEY DEFAULT uuidv7(),
+    conversation_id UUID NOT NULL REFERENCES conversations(id) ON DELETE CASCADE,
+    sender_id UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    content TEXT NOT NULL,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX idx_messages_conversation_id ON messages (conversation_id);
+CREATE INDEX idx_messages_created_at ON messages (created_at DESC);
+
+CREATE TABLE IF NOT EXISTS chatbot_histories (
+    id UUID PRIMARY KEY DEFAULT uuidv7(),
+    user_id UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    question TEXT NOT NULL,
+    answer TEXT NOT NULL,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX idx_chatbot_histories_user_id ON chatbot_histories (user_id, created_at DESC);