Link sorties to the entrée client they pay out against

New field_entree_liee (entity reference, node -> node) on
ligne_comptable, restricted to entrée-type nodes via a custom
EntreeClientSelection plugin -- narrows further to the same client as
the sortie being linked when one is already known, using the
referencing-entity context Drupal's selection handler API passes
through (getSelectionHandler($field, $entity)).

Quick-link UI (per the associates' explicit ask: no need to open the
full ligne_comptable form just for this):
- A chain-link icon next to the edit pencil on versement/achat/
  hébergement rows (the only types that pay out against a client
  invoice) opens LinkEntreeForm, a one-field AJAX modal, reusing the
  same modal/close-on-save plumbing as the edit form. Filled/colored
  when already linked, with the linked entrée's label on hover.
  Also present (states-hidden unless one of those three types is
  selected) on the full node form for whoever's already there anyway.
- Entrée rows get a reconciliation badge once at least one sortie
  links back to them, clickable to drill the table down to just that
  entrée and its linked sorties.

Conformity check assumes multi-compte répartition on both sides (an
entrée's répartition and each linked sortie's répartition can each
split across several comptes -- confirmed this is the real shape of
"hébergement" sorties, e.g. OVH/HETZNER renewals split across all 8
comptes, even though versement/achat lines happen to always be
single-compte in the current data). Per compte, compares the entrée's
répartition share (positive, owed) against the summed répartition of
every linked sortie (negative, paid) -- a residual near zero means
settled, positive means still owed ("reste à verser"), negative means
overpaid ("sur-versé", flagged for a closer look).

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

config/sync/field.field.node.ligne_comptable.field_entree_liee.yml

@@ -0,0 +1,23 @@
+uuid: c2d68287-8e24-4529-a035-39395acca4d3
+langcode: en
+status: true
+dependencies:
+  config:
+    - field.storage.node.field_entree_liee
+    - node.type.ligne_comptable
+id: node.ligne_comptable.field_entree_liee
+field_name: field_entree_liee
+entity_type: node
+bundle: ligne_comptable
+label: 'Entrée client liée'
+description: ''
+required: false
+translatable: true
+default_value: {  }
+default_value_callback: ''
+settings:
+  handler: 'figli_compta_ledger:entree_client'
+  handler_settings:
+    target_bundles:
+      ligne_comptable: ligne_comptable
+field_type: entity_reference