feat: a key that can't be used is explained in the picker

The key picker stays open until the link is made, saying "encrypting
with …" meanwhile. A key that can't be read, or doesn't keep to
share.keyRules, is shown in it in red with which rule it misses
("its value has 28 characters; share.keyRules needs 32
(minLength)"), to pick another.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

internal/ui/app/searchview.go

@@ -61,6 +61,8 @@ type searchView struct {
 	pickLines   []string // what picking is for, above the picker
 	pickHeading string   // the picker's title, on its border
 	pickHelp    []string // inside it, above the tabs
+	pickBusy    string   // what picking is doing, under the help
+	pickErr     string   // why the key picked can't be used
 
 	// loaded are the scopes a search has loaded since the popup opened:
 	// typing loads the scope once, so lists that fail aren't asked for
@@ -438,8 +440,7 @@ func (m *Model) handleSearch(msg tea.KeyPressMsg) tea.Cmd {
 		switch {
 		case v.results && v.res < len(v.shown) && v.pick != nil:
 			r, _ := pickable(v.shown[v.res])
-			m.search = nil
-			return v.pick(m, r)
+			return v.pick(m, r) // the picker closes when it's done
 		case v.results && v.res < len(v.shown):
 			m.search = nil
 			return v.shown[v.res].run(m)
@@ -667,7 +668,9 @@ func (m Model) searchViewBox() string {
 	listH := max(5, min(m.h-10, 14))
 	if v.pick != nil {
 		// What it's for, the help, the tabs and a border more.
-		listH = max(5, min(m.h-10-len(v.pickLines)-len(v.pickHelp)-5, 14))
+		// What it's for, the help, a line or two on the key picked, the
+		// tabs and a border more.
+		listH = max(5, min(m.h-10-len(v.pickLines)-len(v.pickHelp)-8, 14))
 	}
 
 	srcW := 10
@@ -766,6 +769,15 @@ func (m Model) searchViewBox() string {
 		for _, l := range v.pickHelp {
 			body = append(body, " "+l)
 		}
+		switch {
+		case v.pickBusy != "":
+			body = append(body, "", " "+m.st.Notice.Render(v.pickBusy))
+		case v.pickErr != "":
+			body = append(body, "")
+			for _, l := range strings.Split(ansi.Wordwrap(v.pickErr, w-4, " "), "\n") {
+				body = append(body, " "+m.st.Error.Render(l))
+			}
+		}
 		body = append(body, "", " "+m.goToTabs(ts))
 	}
 	body = append(body, " "+v.input.View(), "")