Add signalement (flag) tags for problem lines on /lignes

New field_flag: free-tagging taxonomy reference (multi-value,
auto-create) on ligne_comptable, for marking a line with an
unstructured problem description (e.g. "client impayé") that can't be
detected automatically the way the répartition écart already is.

- New "Signalement" column, inline-editable like Client/Facture/Libellé
  (comma-separated tags, datalist autocomplete, server-side auto-create
  of unknown tags -- same pattern LedgerActionsController already used
  for Client, now shared via findOrCreateTerm()).
- New "Signalées uniquement" filter, mirroring "Écarts uniquement".
- Flagged rows get a distinct amber left-edge accent (box-shadow, not
  border) so a row that's both in écart and signalée shows both
  indicators without one overwriting the other.
- Native node add/edit form gets the field for free via core's
  entity_reference_autocomplete_tags widget.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/modules/custom/figli_compta_ledger/css/home.css

@@ -9,6 +9,7 @@
   --figli-border: #dcdee2;
   --figli-error: #c9312b;
   --figli-positive: #1a7f37;
+  --figli-warning: #b8860b;
   --figli-col-hover: rgba(15, 23, 42, 0.05);
 
   font-family: Inter, -apple-system, sans-serif;
@@ -24,6 +25,7 @@ html.gin--dark-mode #figli-home-app {
   --figli-border: #3d3e42;
   --figli-error: #ff6b6b;
   --figli-positive: #4ade80;
+  --figli-warning: #f0b429;
   --figli-col-hover: rgba(255, 255, 255, 0.07);
 }
 
@@ -205,6 +207,12 @@ html.gin--dark-mode #figli-home-app {
   max-width: 340px;
 }
 
+#figli-home-app td.figli-flag-cell {
+  white-space: normal;
+  min-width: 120px;
+  max-width: 220px;
+}
+
 #figli-home-app tr.figli-group-row td {
   background: var(--figli-bg-alt);
   color: var(--figli-text);
@@ -277,6 +285,27 @@ html.gin--dark-mode #figli-home-app {
   font-weight: 700;
 }
 
+/* Signalé rows: a thick amber accent bar on the left edge, deliberately
+   a different technique from the error row's thin all-around border
+   above (box-shadow, not border) -- so a row that's both in écart *and*
+   signalée shows both indicators at once instead of one overwriting the
+   other's border-left. */
+#figli-home-app tr.figli-flag-row td:first-child {
+  box-shadow: inset 4px 0 0 var(--figli-warning);
+}
+
+#figli-home-app .figli-flag-badge {
+  display: inline-block;
+  padding: 0.05rem 0.4rem;
+  margin: 0 0.2rem 0.15rem 0;
+  border-radius: 8px;
+  font-size: 0.68rem;
+  font-weight: 600;
+  background: color-mix(in srgb, var(--figli-warning) 15%, transparent);
+  color: var(--figli-warning);
+  white-space: nowrap;
+}
+
 /* Column highlight to pair with the row hover, forming a crosshair over
    the hovered cell. box-shadow (not background) so it layers on top of
    whatever the cell already has -- sticky header/footer backgrounds,