EF resolver: resolve by (DF, FID); split EF.ECC and EF.AD per DF

The decoder/encoder lookup now takes an optional DF context and resolves
DF-first, then name, then FID (the spec keys files by FID within their
DF; the name is a display label).  efDfFromPath derives the parent DF
segment of a canonical path.

EF.ECC is split into its two DF-specific decoders: DF.GSM (7F20)
transparent 3n (existing) and ADF.USIM linear-fixed X+4 - the new
efDecEccUsim reads the 3-byte Emergency Call Code, the Annex A alpha and
the Emergency Service Category (decoded per TS 24.008 Table 10.5.135d).
EF.AD is registered as DF-keyed entries (7F20 / ADF.USIM / ADF.ISIM),
reusing the existing encoder.

The df is threaded through the file-manager decoded-view/edit/save and
the snapshot/compare decode.  No ECC editor yet (read-only).

Frontend 1081 + Python 1090 tests green.

frontend/tests/fs_dec_edit.test.js

@@ -52,7 +52,7 @@ const FNS = [
 	'efDecRecordsHtml', 'efDecEditHtml',
 	'efDecCollectValues', 'efDecCollectRows', 'efDecCollectItems',
 	'efBitsSelected', 'pysimFsDecBitsFilter', 'pysimFsDecRowCheck', 'pysimFsDecItemTag', 'pysimFsDecAddItem',
-	'pysimFsDecRemoveItem', 'pysimFsFindNode',
+	'pysimFsDecRemoveItem', 'pysimFsFindNode', 'pysimFsNodePath', 'efDfFromPath',
 	'pysimFsHasDecoder', 'pysimFsHasEncoder', 'pysimFsDecSave', 'pysimFsDecEdit',
 	'pysimFsPillsEnabled', 'pysimFsSyncContentVisibility', 'gsm7Decode',
 	'gsm7TextToSeptets', 'gsm7Encode',
@@ -271,6 +271,19 @@ test('pysimFsHasEncoder resolves the selected file by name or FID', () => {
 	assert.strictEqual(pysimFsHasEncoder(), false);
 });
 
+test('the file-manager resolver call sites pass the node\'s parent DF', () => {
+	// the DF context comes from the node's canonical path; these five sites
+	// gate/read/edit a selected file and must resolve the same entry
+	assert.ok(html.includes('return !!efFindDecoder(node && node.name, fid, df);'));
+	assert.ok(html.includes('return !!efFindEncoder(node && node.name, fid, df);'));
+	assert.ok(html.includes("const df = node ? efDfFromPath(pysimFsNodePath(node)) : '';"));
+	assert.ok(html.includes('const model = efDecEditModel(node && node.name, fid, content,'));
+	for (const fn of ['pysimFsDecSave', 'pysimFsDecAddRow', 'pysimFsDecAddItem']) {
+		assert.ok(/efFindEncoder\([^;]*efDfFromPath\(pysimFsNodePath\(node\)\)/s.test(extractFunc(html, fn)),
+			fn + ' resolves the entry with the node DF');
+	}
+});
+
 test('the Edit decoded button is encoder-gated next to Edit raw', () => {
 	const btn = /<button[^>]*id="pysim-fs-edit-dec-btn"[^>]*>/.exec(html);
 	assert.ok(btn, 'Edit decoded button');