fix(infra): 接入 tauri-plugin-single-instance 防双实例双插入 (closes #50)

[appergb]

问题

两份 OpenLess (`/Applications/OpenLess.app` + dev build) 同时跑时，两进程各自抓全局热键 → 按一次键被识别两次 → 文本插入两份。

修复

`tauri-plugin-single-instance` v2 + 二进程启动回调聚焦已有主窗口。

Test plan

• cargo check 通过
• 手动：从 `/Applications/OpenLess.app` 启动一份，再 `open .../release/bundle/macos/OpenLess.app` → 第二个秒退，第一个被聚焦
• 临时绕过仍可：`pkill -f OpenLess` 再启动想要的那一个

关联

closes #50

Summary by Sourcery

Enforce single-instance behavior for the Tauri desktop app to prevent duplicate processing when multiple builds are running simultaneously.

New Features:

• Integrate the tauri-plugin-single-instance plugin to route secondary launches to the existing main window and exit the new process.

Bug Fixes:

• Prevent duplicate global hotkey handling and double text insertion when multiple OpenLess instances are started.

Build:

• Add tauri-plugin-single-instance as a runtime dependency in the Tauri app Cargo.toml.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Integrates the tauri-plugin-single-instance to enforce a single running instance of the Tauri app and focus the existing main window when a second instance is launched, preventing duplicated hotkey handling and double text insertion, along with the necessary dependency wiring in Cargo.toml/lock.

Sequence diagram for handling a second OpenLess instance launch

sequenceDiagram
    actor User
    participant macOS
    participant SecondInstance
    participant SingleInstancePlugin
    participant FirstInstance
    participant MainWindow

    User->>macOS: Launch OpenLess second instance
    macOS->>SecondInstance: Start process
    SecondInstance->>SingleInstancePlugin: Initialize single instance lock
    SingleInstancePlugin-->>SecondInstance: Detect existing running instance
    SingleInstancePlugin->>FirstInstance: Send activation signal
    FirstInstance->>MainWindow: Call show_main_window
    MainWindow-->>User: Existing main window focused
    SingleInstancePlugin->>SecondInstance: Instruct immediate exit
    SecondInstance-->>macOS: Terminate process

Loading

File-Level Changes

Change	Details	Files
Enforce single-instance behavior in the Tauri application and focus the existing main window when a second instance is launched.	Register the tauri-plugin-single-instance plugin in the Tauri builder pipeline before other plugins. Provide a callback that logs when a second instance launches and calls the existing show_main_window helper to focus the main window of the already-running app.	openless-all/app/src-tauri/src/lib.rs
Add tauri-plugin-single-instance dependency to the Tauri project.	Declare tauri-plugin-single-instance version 2 under [dependencies] in Cargo.toml. Update Cargo.lock to resolve and lock the new dependency graph.	openless-all/app/src-tauri/Cargo.toml openless-all/app/src-tauri/Cargo.lock

Possibly linked issues

• fix: 防止多实例并存导致语音被插入两遍 #50: PR adds tauri-plugin-single-instance and focuses existing window, exactly implementing the issue’s proposed single-instance fix.

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