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>

internal/server/auth.go

@@ -215,6 +215,9 @@ type navItem struct {
 	Name  string
 	Color string
 	Count int
+	// Param is the /partials/inbox query fragment for this item, for example
+	// "category=Action" or "folder=delete" (Phase 4 folder views).
+	Param string
 }
 
 type dashboardData struct {
@@ -250,7 +253,7 @@ func categoryCounts(items []store.MessageListItem, categories []store.Category)
 	return counts
 }
 
-// handleDashboard renders the inbox shell with real category counts.
+// handleDashboard renders the inbox shell with real category and folder counts.
 func (s *Server) handleDashboard(w http.ResponseWriter, r *http.Request) {
 	sess := sessionFrom(r)
 
@@ -266,15 +269,26 @@ func (s *Server) handleDashboard(w http.ResponseWriter, r *http.Request) {
 		s.logger.Error("load dashboard categories", "error", err)
 	}
 	counts := categoryCounts(items, categories)
+	folderCounts, err := s.store.CountByFolder(r.Context())
+	if err != nil {
+		s.logger.Error("load dashboard folder counts", "error", err)
+		folderCounts = nil
+	}
 
 	catNav := make([]navItem, 0, len(categories)+1)
 	for _, c := range categories {
-		catNav = append(catNav, navItem{Name: c.Name, Color: "var(--primary-soft, var(--surface-2))", Count: counts[c.Name]})
+		catNav = append(catNav, navItem{
+			Name:  c.Name,
+			Color: "var(--primary-soft, var(--surface-2))",
+			Count: counts[c.Name],
+			Param: "category=" + url.QueryEscape(c.Name),
+		})
 	}
 	catNav = append(catNav, navItem{
 		Name:  unclassifiedCategory,
 		Color: "var(--ink-faint)",
 		Count: counts[unclassifiedCategory],
+		Param: "category=" + url.QueryEscape(unclassifiedCategory),
 	})
 
 	data := dashboardData{
@@ -285,9 +299,9 @@ func (s *Server) handleDashboard(w http.ResponseWriter, r *http.Request) {
 		Total:      len(items),
 		Categories: catNav,
 		Folders: []navItem{
-			{Name: "Replied-to", Color: "var(--sticker-green)"},
-			{Name: "Delete", Color: "var(--sticker-red)"},
-			{Name: "Saved", Color: "var(--sticker-teal)"},
+			{Name: "Replied-to", Color: "var(--sticker-green)", Count: folderCounts[store.FolderReplied], Param: "folder=" + store.FolderReplied},
+			{Name: "Delete", Color: "var(--sticker-red)", Count: folderCounts[store.FolderDelete], Param: "folder=" + store.FolderDelete},
+			{Name: "Saved", Color: "var(--sticker-teal)", Count: folderCounts[store.FolderSaved], Param: "folder=" + store.FolderSaved},
 		},
 	}
 	w.Header().Set("Content-Type", "text/html; charset=utf-8")