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/spelling.rs

@@ -90,11 +90,17 @@ impl App {
         let received = self.spell_rx.as_ref().and_then(|rx| rx.try_recv().ok());
         if let Some((text, matches)) = received {
             self.spell_rx = None;
-            if self.spell_dict.is_some() {
-                self.spell_status = Self::spell_count_status(matches.len());
-            }
             self.spell_matches = matches;
             self.spell_checked_text = text;
+            // Words the user waved away stay quiet across re-checks.
+            drop_dismissed(
+                &mut self.spell_matches,
+                &self.spell_checked_text,
+                &self.dismissed,
+            );
+            if self.spell_dict.is_some() {
+                self.spell_status = Self::spell_count_status(self.spell_matches.len());
+            }
         }
     }