fix(viewer): byte-faithful saves, poll/save races, clearer errors

- Keep CRLF (or CR) line endings and a UTF-8 BOM through the editor:
  textFormat.ts records the dominant separator and the BOM on load and
  restores both on save, so a save changes only the user's edits.
- A clean document whose reload failed retries on the next poll.
- A poll that overlaps a save, or was issued before one settled, is
  ignored instead of reading the pre-save hash as a change.
- A conflict whose follow-up poll has no hash shows an error with a
  Reload button rather than an Overwrite that could only conflict again.
- Match write.rs's exact read-only message; show the read-only reason as
  visible text; error banners are role="alert".
- vite/client types move to src/vite-env.d.ts.
- Tests: CRLF and BOM saves, reload retry, poll/save race, null-hash
  conflict, Save and close success and failure, and CodeEditor.setDoc
  keeping cursor and scroll.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

app/src/viewer/viewerState.ts

@@ -96,8 +96,11 @@ export function reduceViewer(state: ViewerDocState, action: ViewerAction): Viewe
 /** What EditorPane does after a poll: nothing, reload silently, or show the banner. */
 export function pollEffect(before: ViewerDocState, after: ViewerDocState): "none" | "reload" | "banner" {
   if (after.disk === "gone") return before.disk === "gone" ? "none" : "banner";
-  if (after.disk !== "changed" || after.diskHash === before.diskHash) return "none";
-  return after.doc === "clean" ? "reload" : "banner";
+  if (after.disk !== "changed") return "none";
+  // A clean doc still marked "changed" means its reload failed; retry it
+  // rather than leave stale text under a "Changed on disk" badge.
+  if (after.doc === "clean") return "reload";
+  return after.diskHash === before.diskHash ? "none" : "banner";
 }
 
 export function canSave(state: ViewerDocState, editable: boolean): boolean {