feat: add last-turn diff view

Adds a Last turn scope to DiffView that renders OpenCode snapshot diffs from the latest user message summary without re-fetching git contents. The view hides Review in that mode and carries the selected diff scope through main and context-panel navigation.

Connects latest-turn changed-file chips in chat to the snapshot diff view on desktop and mobile, while keeping older turn chips static/read-only to avoid misleading affordances and extra subscriptions. Updates localized labels and empty states plus changelog.

Validation: bun run type-check (packages/ui); bun run lint (packages/ui).

packages/ui/src/lib/i18n/messages/fr.ts

@@ -1088,6 +1088,7 @@ export const dict = {
   'diffView.state.loadingRepositoryStatus': 'Chargement de l\'état du dépôt...',
   'diffView.state.notGitRepository': 'Pas un dépôt git. Utilisez l\'onglet Git pour initialiser ou modifier des répertoires.',
   'diffView.state.cleanWorkingTree': 'Worktree sans modifications, rien à afficher',
+  'diffView.state.noLastTurnChanges': 'Aucun changement du dernier tour à afficher',
   'diffView.state.failedToLoadDiff': 'Échec du chargement du différentiel',
   'diffView.state.loadingDiff': 'Chargement du différentiel...',
   'diffView.state.loadingChanges': 'Chargement des modifications...',
@@ -1097,6 +1098,7 @@ export const dict = {
   'diffView.summary.changedFilesPlural': 'Fichiers {count} modifiés',
   "diffView.scope.changed": "Modifiés",
   "diffView.scope.staged": "Staged",
+  "diffView.scope.lastTurn": "Dernier tour",
   "diffView.scope.selectorAria": "Sélectionner le mode de changements",
   'diffView.actions.retry': 'Réessayer',
   'diffView.actions.renderAnyway': 'Afficher quand même',