Files view: change details with before/after images (v2.4.0)

- the timeline's Δ glyph became a **Details** button, and it now appears on
  Update rows too (not just card-side changes); EN "Changed (card)" ->
  "Changed on card", RU "Изменено (картой)" -> "Изменено картой"
- the details modal shows the affected unit — the whole file, or the single
  record that changed — **before and after** the change as hex views (16 bytes
  per row, ASCII column, never-observed bytes as `--`), with the bytes that
  changed and the bytes the operation *first observed* highlighted in two
  different colours, plus the changed/new byte counts and the APDU reference;
  the old before/after byte table is gone
- `GET /api/sessions/<id>/files/image?key=…&change=…` returns those two views
  (segments with offsets) plus the change's metadata; the images are
  reconstructed from the current image by undoing the later changes
  (`FileTracker.change_images`), so nothing is duplicated per event — every
  value change is an event, hence the values are exact (a byte only first
  observed later can appear as known in both views)
- tracker: change events carry `observed_ranges` (bytes that were unknown
  before the operation) next to `ranges`; an update that only observes new
  bytes now records an event (so it can be inspected); record-file ranges are
  in-record byte offsets (the record number stays in its own field), which the
  previous "record number as position" could not express for a hex highlight
- tests: change-images reconstruction (before/after per event, later changes
  undone, records isolated, observation-only events, unknown gaps), the image
  endpoint (200/404/400), and Node tests for the hex-image helper (highlight
  classes, unknown gaps, ASCII, row limit) and the modal rendering
- v2.4.0; SW cache simtrace-analyser-v65

simtrace_analyser/database.py

@@ -198,13 +198,22 @@ class Database:
         Returns the tracker's result dict: the operation timeline, per-file
         counters/images/changes, the SFI relations and the AID labels.
         """
+        tracker = self._file_tracker(session_id)
+        return tracker.result()
+
+    def change_images(self, session_id, key, idx):
+        """Before/after images of the unit affected by change *idx* of *key*
+        (the Files view's Details modal), or None for an unknown file/index."""
+        return self._file_tracker(session_id).change_images(key, idx)
+
+    def _file_tracker(self, session_id):
         from .filetrack import FileTracker
         rows = self._conn.execute(
             'SELECT id, session_id, elapsed, type, data, flags FROM messages '
             'WHERE session_id=? ORDER BY elapsed, id', (session_id,)).fetchall()
         tracker = FileTracker()
         self._decode_rows(rows, on_message=tracker.observe)
-        return tracker.result()
+        return tracker
 
     def get_messages_raw(self, session_id):
         rows = self._conn.execute(