feat: H shows what's hidden; Spring keys that don't look secret are hidden

Sources, files and secrets get a Hidden flag. The repo provider marks
Spring keys that match neither pattern, files with only those, and repos
with only such files, instead of leaving them out.

- Hidden items are left out of the panes, Go to and lazysecrets list;
  a pane's counter says how many it hides.
- H (lists.toggleHidden) shows them, dimmed whole in mutedColor;
  list --hidden lists them, json marks them "hidden".
- A revealed empty value shows "∅ no value (an empty string)", muted,
  instead of a blank line.

internal/ui/app/favourites.go

@@ -6,6 +6,7 @@ import (
 	"time"
 
 	tea "charm.land/bubbletea/v2"
+	"github.com/charmbracelet/x/ansi"
 
 	"git.kebcloud.no/keb/lazysecrets/internal/cachefile"
 	"git.kebcloud.no/keb/lazysecrets/internal/expiry"
@@ -116,7 +117,7 @@ func (m Model) containerRender(withSource bool) func(styles.Styles, provider.Con
 			}
 			line += sty.Muted.Render("  " + c.Detail)
 		}
-		line = marks(sty, n, c.Source.Provider, m.recentIcon, m.now()) + line
+		line = dimIf(sty, c.Hidden, marks(sty, n, c.Source.Provider, m.recentIcon, m.now())+line)
 		if withSource {
 			src := c.Source.Name
 			if account := accountOf(c.Source); account != "" {
@@ -140,6 +141,7 @@ func (m Model) objectRender() func(styles.Styles, provider.Object, int) string {
 		if o.Detail != "" {
 			line += sty.Muted.Render("  " + o.Detail)
 		}
+		line = dimIf(sty, o.Hidden, line)
 		switch state, left := m.expiry(o); state {
 		case expiry.Expired:
 			line += " " + sty.Error.Render("✗ expired")
@@ -150,6 +152,15 @@ func (m Model) objectRender() func(styles.Styles, provider.Object, int) string {
 	}
 }
 
+// dimIf draws a hidden item's row (shown with H) in the muted colour,
+// whole, so it stands apart from what's listed by the provider's rules.
+func dimIf(sty styles.Styles, hidden bool, line string) string {
+	if !hidden {
+		return line
+	}
+	return sty.Muted.Render(ansi.Strip(line))
+}
+
 // starredFirst moves starred items to the front, keeping the order
 // otherwise. It doesn't modify items, which may be cached.
 func starredFirst[T any](items []T, starred func(T) bool) []T {