Let a spelling or grammar issue be dismissed

Not every flag deserves a fix, so give the checkers a way to be told no:

- ✖ beside an issue in the panel, and a matching entry in the editor's
  right-click menu, wave that issue away.
- A dismissal is remembered as the offending text paired with the message
  rather than a byte range, since offsets move as soon as you type. Both
  checkers filter their fresh results against it, so a dismissed complaint
  stays gone across re-checks and repeats of the same phrase in the file.
- The panel header counts the dismissals and ↩ takes them back. The offline
  spell check then rebuilds its own list; LanguageTool's can only come from
  the server, so those are dropped with a nudge towards ✓ Check.

Dismissals belong to the open file and the session — they are cleared when
another file or workspace is opened, and never written to disk. A name or
invented term still belongs in the word list, which persists.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011CVsxwa6YukFS2YFUY8W2j

src/app/editor.rs

@@ -197,6 +197,7 @@ impl App {
                         .map(str::to_string)
                 });
                 let mut accept: Option<String> = None;
+                let mut dismiss: Option<usize> = None;
                 output.response.context_menu(|ui| {
                     match &menu {
                         Some((i, reps)) if !reps.is_empty() => {
@@ -215,6 +216,19 @@ impl App {
                             ui.label(egui::RichText::new("No spelling issue here").weak());
                         }
                     }
+                    // Not every complaint is worth acting on — let a deliberate
+                    // one be waved away instead of underlined for good.
+                    if let Some((i, _)) = &menu {
+                        ui.separator();
+                        if ui
+                            .button("✖ Dismiss this issue")
+                            .on_hover_text("Stop flagging this in this file")
+                            .clicked()
+                        {
+                            dismiss = Some(*i);
+                            ui.close_menu();
+                        }
+                    }
                     // A character or place name is not a misspelling; let it be
                     // accepted for good rather than corrected every time.
                     if let Some(word) = &target_word {
@@ -234,6 +248,9 @@ impl App {
                 if let Some(word) = accept {
                     self.add_to_dictionary(&word);
                 }
+                if let Some(i) = dismiss {
+                    self.dismiss_issue(i);
+                }
                 if let Some((i, j)) = chosen {
                     self.apply_current_fix(i, j);
                     self.spell_menu = None;