feat: share env files in --demo

Providers whose containers are files give their contents through
provider.Contents, which sharing reads instead of the disk. The demo
repos build their env files from their keys, and the second demo
account has a key to share with (kv-shared-prod / env-share), so S → f
and opening the link work in --demo; the demo repos aren't on disk,
so opening asks where to save.

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

internal/ui/app/sharefiles.go

@@ -40,9 +40,9 @@ type sealedMsg struct {
 }
 
 // canShareFiles reports whether src's env files can be shared: it's a
-// repo whose files are on disk.
+// repo whose files can be read.
 func (m Model) canShareFiles(src provider.Source) bool {
-	_, ok := m.providerFor(src).(provider.Files)
+	_, ok := m.providerFor(src).(provider.Contents)
 	return src.Kind == provider.KindRepo && ok
 }
 
@@ -50,7 +50,7 @@ func (m Model) canShareFiles(src provider.Source) bool {
 // plain ones.
 func (m *Model) shareFiles(src provider.Source, cs []provider.Container) tea.Cmd {
 	p := m.providerFor(src)
-	files, ok := p.(provider.Files)
+	files, ok := p.(provider.Contents)
 	if !ok {
 		m.flash = warning("these files can't be shared")
 		return nil
@@ -78,16 +78,12 @@ func (m *Model) shareFiles(src provider.Source, cs []provider.Container) tea.Cmd
 			}
 		}
 		for _, c := range cs {
-			f, err := files.File(c, nil)
-			if err == nil {
-				var b []byte
-				b, err = os.ReadFile(f.Path)
-				msg.files = append(msg.files, share.File{Path: c.Name, Data: b})
-			}
+			b, err := files.Contents(ctx, c)
 			if err != nil {
 				msg.err = err
 				return msg
 			}
+			msg.files = append(msg.files, share.File{Path: c.Name, Data: b})
 		}
 		key, ok, err := share.DefaultKey(src.ID, general)
 		if ok {