ui: start the SELECT picker session in MF for both RFM builders

The file picker's implicit current DF now defaults to MF for SIM RFM and
USIM RFM alike (the real context follows the TAR the packet is sent to,
TS 102 226 7.2/7.3, so the default is neutral and the per-row "starts in"
selector covers ADF sessions - ADF.USIM files appear once it is switched).
Tests set the ADF session explicitly where they exercise ADF-relative fills
plus a new default assertion; help 2.1 EN/RU, READMEs and AGENTS updated.
sw cache -> simple-v244; version stays 3.4.0.

frontend/index.html

@@ -3311,7 +3311,10 @@ function rfmFileEntries() {
 // packet is sent to, not on the builder, so the picker lets it be changed.
 function rfmStartDf(chainId) {
 	if (!_rfmStartDf[chainId]) {
-		_rfmStartDf[chainId] = chainKind(chainId) === 'usim' ? 'ADF.USIM' : 'MF';
+		// MF for both builders: the real implicit DF follows the TAR the
+		// secured packet is sent to (TS 102 226 7.2/7.3), so the picker
+		// starts neutral and the per-row selector covers ADF sessions.
+		_rfmStartDf[chainId] = 'MF';
 	}
 	return _rfmStartDf[chainId];
 }