feat: add database support, conversation sidebar, and improve chat streaming

- Update .gitignore to exclude database files, extensions, and .cursor directory
- Enhance chat streaming API with safe enqueue and close functions to prevent errors
- Integrate ConversationSidebar component into ClientHome for better UI
- Add dependencies like better-sqlite3 and esbuild packages for database functionality

This commit introduces database persistence for conversations, improves error handling in streaming responses, and adds a sidebar for managing chats, enhancing overall app robustness and user experience.

database/schema.sql

@@ -0,0 +1,32 @@
+-- Schema inicial do banco de dados OllaHub
+-- Conversas
+CREATE TABLE conversations (
+    id TEXT PRIMARY KEY,
+    title TEXT,
+    model TEXT NOT NULL,
+    created_at INTEGER NOT NULL,
+    updated_at INTEGER NOT NULL
+);
+
+-- Mensagens
+CREATE TABLE messages (
+    id TEXT PRIMARY KEY,
+    conversation_id TEXT NOT NULL,
+    role TEXT NOT NULL CHECK(role IN ('user', 'assistant', 'system')),
+    content TEXT NOT NULL,
+    timestamp INTEGER NOT NULL,
+    FOREIGN KEY (conversation_id) REFERENCES conversations(id) ON DELETE CASCADE
+);
+
+-- Embeddings vetoriais (384 dimensões do Ollama)
+CREATE TABLE embeddings (
+    id TEXT PRIMARY KEY,
+    message_id TEXT NOT NULL,
+    vector BLOB NOT NULL,
+    FOREIGN KEY (message_id) REFERENCES messages(id) ON DELETE CASCADE
+);
+
+-- Índices para performance
+CREATE INDEX idx_messages_conversation ON messages(conversation_id, timestamp);
+CREATE INDEX idx_conversations_updated ON conversations(updated_at DESC);
+CREATE INDEX idx_embeddings_message ON embeddings(message_id);