Phase 4: triage actions (delete, move, mark; bulk select) (AUD-70)

Bulk select in the triage list, with delete/move/mark and a recoverable
delete (FR-6, FR-9).

- migration v4: messages.folder + messages.mailbox; folder/category views
- internal/mailops: app folder -> Gmail label moves over IMAP (IPv4), locate
  by X-GM-MSGID, create labels lazily, move/save/reply/restore, flag marks
- mailfetch: CREATE, UID MOVE (COPY+EXPUNGE fallback), STORE flags, X-GM-MSGID search
- server: POST /actions/bulk with CSRF, UI delete confirmation, second
  confirmation for messages classified Spam (never auto-deleted), per-message
  and summary action-log rows (FR-13)
- inbox: select-all toolbar, checkboxes, folder nav, Restore on non-inbox rows

Co-Authored-By: Paperclip <noreply@paperclip.ing>

web/static/app.css

@@ -375,3 +375,40 @@ a:hover { text-decoration: underline; }
   .category-rename { grid-template-columns: 1fr; }
   .category-remove .btn { width: 100%; }
 }
+
+/* Phase 4: bulk triage toolbar (FR-6) and recoverable-delete views (FR-9) */
+.bulk-toolbar {
+  display: flex;
+  align-items: center;
+  gap: var(--space-sm);
+  flex-wrap: wrap;
+  padding: var(--space-sm) var(--space-md);
+  border-bottom: 1px solid var(--hairline);
+  background: var(--surface);
+}
+.bulk-check {
+  display: inline-flex;
+  align-items: center;
+  gap: var(--space-xs);
+  min-height: 44px;
+  font: var(--type-body-sm);
+  color: var(--ink-secondary);
+}
+.bulk-check input,
+.msg-select {
+  width: 18px;
+  height: 18px;
+  flex: 0 0 auto;
+  accent-color: var(--primary);
+}
+.selected-count { font: var(--type-caption); color: var(--ink-faint); }
+.bulk-actions { display: flex; align-items: center; gap: var(--space-xs); flex-wrap: wrap; }
+.view-label {
+  margin-left: auto;
+  font: var(--type-eyebrow);
+  text-transform: uppercase;
+  letter-spacing: .125px;
+  color: var(--ink-faint);
+}
+.btn-small { min-height: 32px; padding: 0 var(--space-sm); font: var(--type-caption); }
+.scan-note-error { color: var(--sticker-red); }