feat(settings): add auto-launch on system startup feature

Implement auto-launch functionality with proper state synchronization
and error handling across Windows, macOS, and Linux platforms.

Key changes:
- Add auto_launch module using auto-launch crate 0.5
- Define typed errors (AutoLaunchPathError, AutoLaunchEnableError, etc.)
- Sync system state with settings.json on app startup
- Only call system API when auto-launch state actually changes
- Add UI toggle in Window Settings panel
- Add i18n support for auto-launch settings (en/zh)

Implementation details:
- Settings file (settings.json) is the single source of truth
- On startup, system state is synced to match settings.json
- Error handling uses Rust type system with proper error propagation
- Frontend optimized to avoid unnecessary system API calls

Platform support:
- Windows: HKEY_CURRENT_USER registry modification
- macOS: AppleScript-based launch item (configurable to Launch Agent)
- Linux: XDG autostart desktop file

src-tauri/Cargo.lock

@@ -291,6 +291,17 @@ version = "1.1.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1505bd5d3d116872e7271a6d4e16d81d0c8570876c8de68093a09ac269d8aac0"
 
+[[package]]
+name = "auto-launch"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1f012b8cc0c850f34117ec8252a44418f2e34a2cf501de89e29b241ae5f79471"
+dependencies = [
+ "dirs 4.0.0",
+ "thiserror 1.0.69",
+ "winreg 0.10.1",
+]
+
 [[package]]
 name = "autocfg"
 version = "1.5.0"
@@ -598,6 +609,7 @@ name = "cc-switch"
 version = "3.7.0"
 dependencies = [
  "anyhow",
+ "auto-launch",
  "chrono",
  "dirs 5.0.1",
  "futures",
@@ -982,6 +994,15 @@ dependencies = [
  "subtle",
 ]
 
+[[package]]
+name = "dirs"
+version = "4.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ca3aa72a6f96ea37bbc5aa912f6788242832f75369bdfdadcb0e38423f100059"
+dependencies = [
+ "dirs-sys 0.3.7",
+]
+
 [[package]]
 name = "dirs"
 version = "5.0.1"
@@ -1000,6 +1021,17 @@ dependencies = [
  "dirs-sys 0.5.0",
 ]
 
+[[package]]
+name = "dirs-sys"
+version = "0.3.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1b1d1d91c932ef41c0f2663aa8b0ca0342d444d842c06914aa0a7e352d0bada6"
+dependencies = [
+ "libc",
+ "redox_users 0.4.6",
+ "winapi",
+]
+
 [[package]]
 name = "dirs-sys"
 version = "0.4.1"
@@ -6397,6 +6429,15 @@ dependencies = [
  "memchr",
 ]
 
+[[package]]
+name = "winreg"
+version = "0.10.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "80d0f4e272c85def139476380b12f9ac60926689dd2e01d4923222f40580869d"
+dependencies = [
+ "winapi",
+]
+
 [[package]]
 name = "winreg"
 version = "0.52.0"