Add clean shutdown, wallet safety, and UI contrast fixes

Shutdown:
- Call litelib_shutdown() to stop Rust background threads on exit
- Add 15-second timeout on wallet save dialog to prevent hang on close
- Add litelib_shutdown FFI declaration in header and controller

UI Contrast (dragonx theme):
- Fix disabled buttons: white text was invisible on white background
- Add QWizard, QMessageBox, QTextBrowser, QPlainTextEdit styling for dark theme
- Add QCheckBox, QRadioButton, QDialogButtonBox contrast rules
- Fix seed word verification buttons: dark themed with explicit text color
- Fix chat bubbles: replace light backgrounds with dark themed colors
- Fix Terms of Service link color: #0000ff -> #6699ff for visibility
- Remove duplicate conflicting QLabel#lblMessage CSS rule

Add v1.1.0 release notes with checksums

lib/src/lib.rs

@@ -290,6 +290,20 @@ pub extern "C" fn litelib_check_server_online(server: *const c_char) -> bool {
     }
 }
 
+/// Cleanly shut down the light client, stopping mempool monitor threads.
+/// Must be called before exit to prevent hangs.
+#[no_mangle]
+pub extern "C" fn litelib_shutdown() {
+    let lc_option = match LIGHTCLIENT.lock() {
+        Ok(l) => l.borrow().clone(),
+        Err(poisoned) => poisoned.into_inner().borrow().clone(),
+    };
+
+    if let Some(lc) = lc_option {
+        lc.shutdown();
+    }
+}
+
 /**
  * Callers that receive string return values from other functions should call this to return the string 
  * back to rust, so it can be freed. Failure to call this function will result in a memory leak