Add sous-traitant, salaire/stage, and charges local pro ligne types

Three new field_type_ligne values (config/sync +
figli_compta_ledger.install for fresh-install parity), wired through
every place that enumerates the type list: LedgerActionsController's
inline type-change endpoint, home.js's type dropdown/badge, dashboard.js's
per-type chart, home.css's badge colors.

Sous-traitant is linkable to field_entree_liee (pays out against a
client's work, like versement/achat); salaire/stage and charges local
pro are not (structural costs, like charge). Turns out 13 lines
already carried "salaire_stage" and 1 "sous_traitant" as raw field
values from the historical migration -- list_string doesn't enforce
allowed_values at the storage level, so they saved fine but had no
label and weren't selectable in the UI until now.

Also fixes a real bug this surfaced: filtering /lignes by a sparse
type (e.g. "Autre") silently broke the sliding window -- so few rows
matched that the table no longer overflowed, so it never fired another
'scroll' event, so loadOlder()/loadNewer() never ran again ("les lignes
antérieures ne chargent plus"). Added ensureScrollable(), which keeps
extending the window in both directions whenever a thinning filter
(compte/client/type/écarts) leaves too little to scroll, and widened
the trim cap while filtering (MAX_LOADED_MONTHS_FILTERED) since the
normal 30-month cap actively fights a sparse filter -- extending one
end and immediately trimming the other nets out to nearly the same
slice every round. Bounded by a round counter rather than "did the
window stop moving": addMonths() uses Date#setMonth(), which isn't
invertible for month-end dates, so the window can drift indefinitely
in tiny steps without ever exactly repeating.

Verified: filtering by "Autre" now finds 24 matches (was stuck at 1)
and the view becomes scrollable within ~17s, settling cleanly rather
than hanging.

web/modules/custom/figli_compta_ledger/js/dashboard.js

@@ -18,6 +18,9 @@
     versement: 'Versement freelance',
     achat: 'Achat client',
     hebergement: 'Hébergement',
+    sous_traitant: 'Sous-traitant',
+    salaire_stage: 'Salaire / stage',
+    charges_local_pro: 'Charges local pro',
     autre: 'Autre',
   };
   // Stable colour per type, independent of sort order -- a viewer
@@ -29,6 +32,9 @@
     versement: '#d97a0a',
     achat: '#3b6fe0',
     hebergement: '#0e9182',
+    sous_traitant: '#c9312b',
+    salaire_stage: '#0891b2',
+    charges_local_pro: '#65a30d',
     autre: '#9061f0',
   };