feat(snippets): initialize snippet db

This commit creates the initial backend infrastructure for the snippets feature. It sets up the core data model, a dedicated `SnippetManager` for database interactions using `rusqlite`, and integrates it into the Tauri application state.

src-tauri/src/snippets/manager.rs

@@ -0,0 +1,36 @@
+use crate::error::AppError;
+use rusqlite::{Connection, Result as RusqliteResult};
+use std::sync::Mutex;
+use tauri::{AppHandle, Manager};
+
+pub struct SnippetManager {
+    db: Mutex<Connection>,
+}
+
+impl SnippetManager {
+    pub fn new(app_handle: AppHandle) -> Result<Self, AppError> {
+        let data_dir = app_handle
+            .path()
+            .app_local_data_dir()
+            .map_err(|_| AppError::DirectoryNotFound)?;
+        let db_path = data_dir.join("snippets.sqlite");
+        let db = Connection::open(db_path)?;
+        Ok(Self { db: Mutex::new(db) })
+    }
+
+    pub fn init_db(&self) -> RusqliteResult<()> {
+        let db = self.db.lock().unwrap();
+        db.execute(
+            "CREATE TABLE IF NOT EXISTS snippets (
+                id INTEGER PRIMARY KEY AUTOINCREMENT,
+                name TEXT NOT NULL,
+                keyword TEXT NOT NULL UNIQUE,
+                content TEXT NOT NULL,
+                created_at INTEGER NOT NULL,
+                updated_at INTEGER NOT NULL
+            )",
+            [],
+        )?;
+        Ok(())
+    }
+}

src-tauri/src/snippets/mod.rs

@@ -1 +1,3 @@
-pub mod input_manager;
+pub mod input_manager;
+pub mod manager;
+pub mod types;

src-tauri/src/snippets/types.rs

@@ -0,0 +1,13 @@
+use chrono::{DateTime, Utc};
+use serde::Serialize;
+
+#[derive(Serialize, Clone, Debug)]
+#[serde(rename_all = "camelCase")]
+pub struct Snippet {
+    pub id: i64,
+    pub name: String,
+    pub keyword: String,
+    pub content: String,
+    pub created_at: DateTime<Utc>,
+    pub updated_at: DateTime<Utc>,
+}