Add case-sensitive and whole-word toggles to find-in-page #13

Find-in-page works but always matches case-insensitively, with no way to change it. Ctrl+F in any other browser has these toggles.

Where the code is

The matching happens in an injected script, not in Rust. src-tauri/src/commands/browser/scripts/chrome_features.js defines window.__zynlexFind(query), which calls a findAll(query) helper and highlights the results.

The Rust side is a thin wrapper. src-tauri/src/commands/browser/find.rs has browser_find, browser_find_next and browser_stop_find, and they just build a JS call as a string and evaluate it.

The UI is src/components/browser/FindBar.tsx.

What needs doing

1. Add two toggle buttons to FindBar.tsx. Aa for case sensitivity, and something for whole word.
2. Thread the two booleans through browser_find in find.rs. Note that the JS call is built by string formatting, so the query already goes through js_string_literal for escaping. Keep using it.
3. Update findAll in chrome_features.js to respect both flags. Whole-word matching usually means a regex with \b boundaries, but be careful escaping the user query before putting it in a regex, it is arbitrary input.
4. Re-run the search when either toggle changes so results update immediately.

Worth knowing

• The existing highlight logic wraps matches with range.surroundContents(mark). It is already inside a try/catch because that call throws when a range crosses element boundaries. Do not remove that.
• The result count reported back to the UI needs to stay correct after filtering.
• Keep the toggles keyboard-reachable, Ctrl+F users tend not to touch the mouse.

Reasonable first issue if you want to touch a bit of Rust and a bit of frontend without needing to understand the WebView2 COM layer.