feat: E edits the config file

E opens your config like e opens a file: in the nvim lazysecrets runs
in, else in $VISUAL or $EDITOR, else in the system's default app. A
missing config is made first, with a link to its docs. Closing the
editor says to restart lazysecrets to use the changes.

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

internal/ui/app/app.go

@@ -965,6 +965,8 @@ func (m *Model) handleKey(msg tea.KeyPressMsg) (cmd tea.Cmd, quit bool) {
 		return m.refresh(), false
 	case key.Matches(msg, k.Update):
 		return m.update(), false
+	case key.Matches(msg, k.EditConfig):
+		return m.editConfig(), false
 	}
 	return nil, false
 }