Fix back navigation after modal fullscreen, fix SQL operator precedence

Navigation:
- Stale {modal:true}/{chartFull:true} history entries after app restart
  caused back gesture to do nothing (no screen to render, no modal open).
  Now global popstate handler skips these stale entries with history.back().

Rust seed import:
- Fixed SQL operator precedence in nutrients_guessed UPDATE:
  WHERE (guessed IS NULL OR guessed = 0) AND name_lower IN (...)
  was previously parsed as: guessed IS NULL OR (guessed = 0 AND ...)
  which matched ALL products with NULL guessed regardless of name.

frontend/js/main.js

@@ -3008,9 +3008,14 @@ function esc(str) {
 window.addEventListener("popstate", (e) => {
   // If a modal is open, don't handle here (modal has its own handler)
   if (document.querySelector(".modal-overlay")) return;
+  // Stale modal/chart entries left after app restart — skip them
+  if (e.state && (e.state.modal || e.state.chartFull)) {
+    history.back();
+    return;
+  }
   // Pop our nav stack and navigate to previous screen
   if (navStack.length > 1) {
-    navStack.pop(); // remove current
+    navStack.pop();
     const prev = navStack[navStack.length - 1];
     renderScreen(prev, true);
   } else if (e.state && e.state.screen) {

src-tauri/src/lib.rs

@@ -242,7 +242,7 @@ fn import_seed_products(app: tauri::AppHandle) -> Result<String, String> {
         // Sync nutrients_guessed flag
         let _ = main_db.execute_batch(
             "UPDATE main.products SET nutrients_guessed = 1
-             WHERE nutrients_guessed IS NULL OR nutrients_guessed = 0
+             WHERE (nutrients_guessed IS NULL OR nutrients_guessed = 0)
              AND name_lower IN (SELECT s.name_lower FROM seed.products s WHERE s.nutrients_guessed = 1)"
         );
         // Sync micronutrients for products that have them in seed but not in main