fix(taildrop): restore incoming file progress notifications

The io.Copy in PutFile was writing directly to wc, bypassing the
incomingFile wrapper whose Write method increments f.copied and fires
a throttled sendFileNotify on progress. As a result, notifyIncomingFiles
on the JS side only ever fired once (on completion) with received=0,
making progress UI impossible. The original inFile wrapping was lost
during the Android SAF refactor.

Also surface the PartialFile.Done flag through jsIncomingFile so JS can
distinguish the final "transfer complete" notification from in-progress
updates.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

cmd/tsconnect/wasm/wasm_js.go

@@ -405,6 +405,7 @@ func (i *jsIPN) run(jsCallbacks js.Value) {
 					Started:      f.Started.UnixMilli(),
 					DeclaredSize: f.DeclaredSize,
 					Received:     f.Received,
+					Done:         f.Done,
 				}
 			}
 			if b, err := json.Marshal(files); err == nil {
@@ -967,6 +968,7 @@ type jsIncomingFile struct {
 	Started      int64  `json:"started"`      // Unix milliseconds; use new Date(started) in JS
 	DeclaredSize int64  `json:"declaredSize"` // -1 if unknown
 	Received     int64  `json:"received"`     // bytes received so far
+	Done         bool   `json:"done"`         // true once the file has been fully received
 }
 
 // jsOutgoingFile is the JSON representation of an outgoing file transfer