refactor: remove screenshot functionality and headless_chrome dependency

Remove the screenshot capture system and associated UI components to simplify the codebase.

- Remove screenshot.rs command module and related functionality
- Remove headless_chrome dependency from Cargo.toml
- Update Cargo.lock to reflect dependency changes
- Remove screenshot handlers and UI from WebviewPreview component
- Clean up screenshot-related API calls and imports
- Remove camera icon and capture controls from preview interface

This reduces bundle size and eliminates an underutilized feature.

src-tauri/Cargo.toml

@@ -43,7 +43,6 @@ futures = "0.3"
 async-trait = "0.1"
 tempfile = "3"
 which = "7"
-headless_chrome = { version = "1.0", features = ["fetch"] }
 sha2 = "0.10"
 zstd = "0.13"
 uuid = { version = "1.6", features = ["v4", "serde"] }