feat: offline file list + SELECT picker for the SIM/USIM RFM builders (v3.4.0)

The SELECT rows (compact RFM chains and the Expanded Script C-APDU picker,
which shares the row editor) now have a file picker instead of typing FIDs,
paths or chains by hand.

Data:
- `pysim_simple_server/uicc_files.py` builds the standard file list cardless
  from pySim's profiles and application classes (CardProfileUICC + CardProfileSIM
  for the MF tree, every concrete CardApplication subclass for the ADFs) and
  writes `frontend/uicc_files.json` (490 entries: canonical FID path, symbolic
  name, fid, kind, root, ADF AID).  `tests/test_uicc_files.py` regenerates it
  and fails when pySim adds or renames files.  The asset is precached by the
  service worker, so the builders keep working offline.

Picker:
- Sources merged per canonical path: the loaded file-manager tree (card names
  and probed presence; probed-absent files hidden), custom files, and the
  shipped standard list (specs-default until "Probe all files" has run).
- Default list shows what the current method can express; "all files" reveals
  the rest, and picking one auto-switches the method - preferring path (one
  SELECT) over chain - with a note line explaining the switch.  A "starts in"
  selector sets the implicit current DF (UICC shared-FS RFM app starts in MF,
  an ADF RFM app in its ADF, TS 102 226 7.2/7.3 - the TAR decides; default per
  builder, overridable per row).
- Fill rules: by FID only for direct children of the current DF; path = FID
  sequence from MF without the MF identifier (ISO 7816-4) or the relative tail
  (USIM P1=09); chain stays relative and follows the TS 102 221 11.1.1.2 FID
  search order (children, parent, siblings), so no hop to the common ancestor.
  ADF roots are not pickable (selection is by AID; TS 102 226 7.1 forbids
  P1=04 for RFM) - the By AID method stays manual.

Tests/docs: frontend/tests/uicc_files.test.js (asset shape, merge/priority/
exclusion, fill matrix, relative chains, session-context tracking, option
grouping); help 2.1/2.2 EN+RU, READMEs, AGENTS.  sw cache -> simple-v242.

README.md

@@ -77,6 +77,15 @@ CLA = `A0` (GSM 11.11 / ISO 7816-4).
 | By DF name / AID | 04 | 00 | AID (application ID) |
 | ADF RFM chain | 00 | 00 | Comma-separated FIDs, each selected in turn |
 
+#### SELECT file picker
+
+Every SELECT row offers a file picker: a filter box, an **all files** toggle, the session start root with the current DF, and the file list grouped by root (`MF`, `ADF.USIM`, ...). Picking a file fills the fields for the current method; when the method cannot express the selection the picker switches to one that can - preferring **path** (one SELECT), then **chain** - and says so, e.g. `7F106F40` (path from MF) or `7F20,6F46` (relative FID chain).
+
+- **List source**: with a card equipped the loaded file-manager tree wins (card names, probed presence; probed-absent files are hidden). Without a card, or for branches the tree has not loaded, the shipped standard list is used: `uicc_files.json`, generated from pySim's profiles/application classes by `pysim_simple_server/uicc_files.py` and drift-guarded by `tests/test_uicc_files.py`. It is specs-default until **Probe all files** runs in the file manager. Custom files are always merged.
+- **Session start**: the implicit current DF follows the TAR the secured packet is sent to (UICC Shared File System RFM -> MF, TS 102 226 §7.2; ADF RFM -> its ADF, §7.3). Defaults: MF here, ADF.USIM for USIM RFM; changeable per row.
+- **Path** is the FID sequence from MF without the MF identifier (ISO 7816-4); the USIM "from current DF" variant uses the relative tail. **Chain** stays relative to the current DF and follows the TS 102 221 §11.1.1.2 FID search order (children, parent, siblings).
+- ADF roots are not pickable - an application is selected by AID, which the **By AID** method keeps manual (TS 102 226 §7.1 forbids P1=`04` for RFM).
+
 #### Options
 
 - **Start with SELECT** — checkbox to prepend a SELECT command before the operation. When unchecked, the operation is sent standalone with CLA.