Files view: the full DF chain in the file path (v2.7.6)

- the tracker kept only the immediate parent DF, so a phonebook file read as
  "DF_PHONEBOOK/4FA1" — the trace's own selection path (00a4080406
  7F105F3A4FA1) spells out the whole chain; the channel state now carries it
  (selected_df_state() returns (df, path), e.g. ('5f3a', ['7f10', '5f3a'])),
  the tracker stores it per file and _file_path() renders it:
  "DF_TELECOM/DF_PHONEBOOK/4FA1"
- chain rules: a child DF selected by FID appends to the current chain, MF and
  the ADF restart it, an AID is its own root, a path selection uses the DFs
  in the path (an explicit '7fff' collapsing to the ADF), and an EF selects
  keeps it.  A leading MF is implicit in a longer path; MF-only files keep
  "MF/…", ADF files "ADF/…" (the previous labels unchanged)
- the chain is learned from the FCP sighting too and extends a shorter path
  recorded earlier, so entries created from a GET RESPONSE still get the full
  path
- verified on the live traces (sessions 47/193): 5f3a/4fa1 ->
  DF_TELECOM/DF_PHONEBOOK/4FA1, 5f3a/4f30 -> DF_TELECOM/DF_PHONEBOOK/EF_PBR
  (4F30), while 3f00/2fe2 -> MF/EF_ICCID (2FE2) and 7fff/6f07 ->
  ADF/EF_IMSI (6F07) stay as before
- tests: selected_df_state (path/FID/MF/ADF/AID/EF cases) and a tracker flow
  with a path selection asserting the full path; 529 Python + 76 Node tests
- README/README_RUS show the chain; PWA_VERSION/pyproject/version.py 2.7.6,
  SW cache simtrace-analyser-v86

README.md

@@ -216,8 +216,10 @@ new messages pin the view to the bottom only while the reader is already
 there, so a jump is never pulled away or un-highlighted by the live poll).  Rows that carry a recorded change (a
 card-side change, or an update that wrote or first observed bytes) also offer
 **Show diff**: a modal showing the full file path (`MF/EF_ICCID (2FE2)`,
-`ADF/EF_IMSI (6F07)`, `DF_GSM_ACCESS/EF_KcGPRS (4F52)`, `AID …/4F09` — the DF
-named from the EF.DIR labels when known) and the affected unit — the whole
+`ADF/EF_IMSI (6F07)`, `DF_TELECOM/DF_PHONEBOOK/4FA1`, `AID …/4F09` — the whole
+DF chain the trace's selection path spells out, each DF named from the
+specification dictionary and the AID from the EF.DIR labels when known) and
+the affected unit — the whole
 file, or the single record that changed — **before and after** the change, as
 hex views (up to 16 bytes per row — a shorter file/record ends its row there
 instead of padding with `--`, and the offset column only appears when a view