Files view: per-file tracking (counters, image, device/card changes)

- new `simtrace_analyser/filetrack.py`: a single-pass tracker over a
  session's decoded messages, keyed by (DF, FID) and trace-wide (resets only
  wipe the per-channel selection): counters (`select`/`read`/`update`,
  successful operations only), a sparse image of the observed bytes
  (transparent files by offset, record files per record number) and the
  change log
- changes: **device** = an UPDATE seen in the trace (applied to the image,
  `no_change` flags a provable no-op); **card** = a READ whose bytes differ
  from the image on bytes already known (logged at the surfacing read with
  the changed ranges and the before/after hex; never-seen bytes just fill
  the image, they are an observation, not a change)
- SFI-addressed accesses join the same entry as path/FID ones: the SFI ↔ FID
  relations come from the normative tables and from every surfaced FCP `88`
  DO (including the spec's "SFI = 5 LSBs of the FID" rule when the DO is
  absent); an SFI used before its relation is learned stays provisional and
  merges into the resolved entry
- the DF identity follows TS 102 221 §8.4/Table 8.2: `selected_df_fid()` now
  resolves an EF path selection to its parent DF and returns `aid:<hex>` for
  applications selected by an unknown AID (named from EF.DIR when the trace
  surfaced it); `Database._decode_rows` gained an `on_message` hook and
  `track_files()`
- `GET /api/sessions/<id>/files`: the operation timeline, the per-file
  counters/coverage/change log, the SFI relations and the AID labels
- PWA: the side panel's Map/Stats tabs became a view selector (Map / Stats /
  Files); the Files view is a timeline of Read / Update / Changed (card) rows
  (colour-coded, the same file names as the Map view), a row click jumps to
  the APDU (loading the pages it needs) and a card-change row's Δ opens the
  changed ranges with the previous and the new bytes; EN/RU
- bounds: the image freezes past 64 KB of observed bytes per file, the change
  log keeps the last 1000 events per file (counters keep counting)
- tests: tests/test_filetrack.py (counters, resets, channels, image/diff
  semantics, record files, SFI resolution and the provisional merge, EF.DIR
  labels, caps, the endpoint) and Node tests for the Files-view helpers and
  wiring
- v2.3.0; MIN_SERVER_VERSION 2.3.0; SW cache simtrace-analyser-v63

README.md

@@ -186,6 +186,35 @@ one.
 Exchanges larger than 255 bytes (extended-length APDUs) cannot be represented
 in the stored wire shape and are skipped with a note in the import report.
 
+### Files view (per-file tracking)
+
+The Trace tab's side panel has a view selector (*Map* / *Stats* / **Files**;
+a drop-down, since three tab captions no longer fit).  The Files view is a
+trace-wide timeline of file operations — every **Read**, **Update** and
+**Changed (card)** row shows the same file name as the Map view, and clicking
+a row jumps to the APDU in the trace.  A *Changed (card)* row carries a Δ
+button that opens the changed ranges with the previous and the new bytes.
+
+The data comes from `simtrace_analyser/filetrack.py`
+(`GET /api/sessions/<id>/files`), a single-pass tracker over the decoded
+session that keeps, keyed by (DF, FID) and **across card resets**: access
+counters (`select`/`read`/`update`, successful operations only), a sparse image
+of the observed contents and the change log.  Device-initiated changes are the
+UPDATE operations seen in the trace; card-initiated ones are inferred when a
+read returns bytes differing from what the image already knew — bytes never
+seen before just fill the image (an observation, not a change).  Files reached
+by SFI share the entry of their path/FID accesses: the SFI ↔ FID relations come
+from the normative tables (TS 102 221 Annex H, TS 31.102 Annex H) and from every
+surfaced FCP carrying the `88` DO, including the spec's "SFI = the 5 LSBs of the
+FID" rule when the DO is absent; an SFI used before its relation is learned
+stays provisional and merges into the resolved entry.  A file's DF context
+follows TS 102 221 §8.4/Table 8.2 (selecting an EF leaves its parent DF current,
+a path selection included); applications selected by an unknown AID get the AID
+as their DF identity, named from EF.DIR when the trace surfaced it.  Bounds: the
+image freezes past 64 KB of observed bytes per file (`image_truncated`) and the
+change log keeps the last 1000 events per file (`changes_total` keeps counting).
+Counters are returned by the API but not shown in this view yet.
+
 Server options:
 
 ```