feat(comment): suggestion diff block + Apply button + mutation (#315 phase 5)

Client UI for agent comment suggestions.

- IComment gains suggestedText / suggestionAppliedAt / suggestionAppliedById.
- comment-list-item shows a "было → стало" block (old selection struck/red, new
  suggestedText green) for a top-level comment with a suggestion, plus an Apply
  button — gated by canShowApply(comment, canEdit): edit permission AND a
  suggestion AND not applied AND not resolved AND top-level. Once applied, an
  "Applied" badge replaces the button.
- canEdit comes from page.permissions.canEdit (real edit permission, NOT the
  looser canComment) and is threaded through CommentListItem and nested
  ChildComments; fail-closed when undefined.
- useApplySuggestionMutation posts to /comments/apply-suggestion; on success it
  writes the applied + server auto-resolve fields into the react-query cache
  (UI flips to Applied + resolved without a refetch); on 409 it shows a specific
  message with the server's currentText, else a generic error.
- i18n keys added in en-US + ru-RU.

Tests (comment-list-item.test.tsx + canShowApply unit suite): Apply visibility
across canEdit/applied/resolved/reply, click dispatches the mutation, diff
rendering. 34 passed.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/client/src/features/comment/components/comment.module.css

@@ -21,6 +21,38 @@
     box-sizing: border-box;
 }
 
+/* Suggested-edit (#315) "было → стало" diff block. */
+.suggestionBlock {
+    margin-top: 8px;
+    margin-left: 6px;
+    padding: 6px;
+    border-radius: var(--mantine-radius-sm);
+    border: 1px solid var(--mantine-color-default-border);
+    overflow-wrap: break-word;
+    word-break: break-word;
+    max-width: 100%;
+    box-sizing: border-box;
+    display: flex;
+    flex-direction: column;
+    align-items: flex-start;
+}
+
+.suggestionOld {
+    text-decoration: line-through;
+    color: var(--mantine-color-red-7);
+    background: var(--mantine-color-red-light);
+    border-radius: 2px;
+    padding: 1px 3px;
+}
+
+.suggestionNew {
+    color: var(--mantine-color-green-9);
+    background: var(--mantine-color-green-light);
+    border-radius: 2px;
+    padding: 1px 3px;
+    margin-top: 4px;
+}
+
 .commentEditor {
 
     &[data-editable][data-surface="muted"] .ProseMirror:not(.focused) {