chore: prepare v3.0.0 release

- Bump version to 3.0.0 across all files
- Update Cargo.toml with proper package metadata
- Rename crate from 'app' to 'cc-switch'
- Use Rust edition 2024 with minimum rust-version 1.85.0
- Update library name to cc_switch_lib

package.json

@@ -1,6 +1,6 @@
 {
   "name": "cc-switch",
-  "version": "3.0.0-beta.1",
+  "version": "3.0.0",
   "description": "Claude Code 供应商切换工具",
   "scripts": {
     "dev": "pnpm tauri dev",