feat: add restore/unarchive for archived sessions

Archived sessions had no way back to the active list: the only available
action was "Delete permanently". Add restore per session (sidebar context
menu, Archive page row) and in bulk (sidebar selection bar).

The OpenCode server cannot clear time.archived over HTTP — session.update
only applies the field for a finite number, so an omitted key is a no-op
and null is silently ignored (verified against opencode 1.18.12). Restore
therefore writes time.archived = 0: every client-side reader classifies
archive state by truthiness, so 0 reads as active in the UI, the event
reducer, and the OpenCode app/TUI.

The server's time_archived IS NULL list filter still excludes such rows,
so the global session cache no longer issues an archived:false request
for its active list. Full and per-directory loads now fetch once with
the inclusive flag and split client-side via splitGlobalSessionsByArchived,
which also halves per-directory refresh requests. Directory bootstrap
keeps the server filter because live child stores must not hold archived
sessions; a restored session re-enters its live store through the
authoritative session.updated event.

unarchiveSession/unarchiveSessions follow the archiveSession contract:
wait for server confirmation before reconciling stores, runtime-guard
every reconciliation, preserve partial batch results, and fail loudly
when the server keeps the session archived instead of toasting a
successful no-op.

Closes #2346

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

@@ -285,6 +285,7 @@ export const dict = {
   'sessions.archivePage.deleteProject': 'Supprimer toutes les sessions archivées de ce projet',
   'sessions.archivePage.deleteProjectAria': 'Supprimer toutes les sessions archivées de {label}',
   'sessions.archivePage.deleteSessionAria': 'Supprimer {title}',
+  'sessions.archivePage.restoreSessionAria': 'Restaurer {title}',
   'sessions.switcher.openAria': 'Sélecteur de session ouvert',
   'sessions.switcher.empty': 'Aucune session récente',
   'sessions.switcher.draftTitle': 'Nouvelle session',
@@ -306,6 +307,11 @@ export const dict = {
   'sessions.sidebar.bulkActions.archivedPlural': 'Sessions {count} archivées',
   'sessions.sidebar.bulkActions.failedArchiveSingle': 'Échec de l\'archivage de la session {count}',
   'sessions.sidebar.bulkActions.failedArchivePlural': 'Échec de l\'archivage des sessions {count}',
+  'sessions.sidebar.bulkActions.restore': 'Restaurer',
+  'sessions.sidebar.bulkActions.restoredSingle': 'Session {count} restaurée',
+  'sessions.sidebar.bulkActions.restoredPlural': 'Sessions {count} restaurées',
+  'sessions.sidebar.bulkActions.failedRestoreSingle': 'Échec de la restauration de la session {count}',
+  'sessions.sidebar.bulkActions.failedRestorePlural': 'Échec de la restauration des sessions {count}',
   'sessions.sidebar.folders.none': 'Aucun dossier pour l\'instant',
   'sessions.sidebar.folders.newFolderEllipsis': 'Nouveau dossier...',
   'sessions.sidebar.folders.removeFromFolder': 'Supprimer du dossier',
@@ -409,6 +415,8 @@ export const dict = {
   'sessions.sidebar.session.delete.error': 'Échec de la suppression de la session',
   'sessions.sidebar.session.archive.success': 'Session archivée',
   'sessions.sidebar.session.archive.error': 'Échec de l\'archivage de la session',
+  'sessions.sidebar.session.restore.success': 'Session restaurée',
+  'sessions.sidebar.session.restore.error': 'Échec de la restauration de la session',
   'sessions.sidebar.group.pr.checksPassed': 'Contrôles {success}/{total} réussis',
   'sessions.sidebar.group.pr.failingCount': 'Échec de {count}',
   'sessions.sidebar.group.pr.pendingCount': '{count} en attente',