feat(fusion_accounting_documents): Documents app <-> invoice bridge

Replaces Enterprise's documents_account with a Fusion-native bridge.
When a PDF/image lands in the Documents app, users can convert it
into a draft vendor bill via a wizard that copies the document's
binary onto the new account.move and posts a chatter note linking
back to the source document.

Adds:
- documents.document.move_id (Many2one to the linked invoice)
- documents.document.is_invoice_candidate (computed; True for
  unlinked PDF/image binaries)
- documents.document.action_create_invoice() opens the wizard
- account.move.source_document_ids reverse linkage + statinfo button
- fusion.create.invoice.from.document.wizard (TransientModel + form)
- ir.actions.server bound to documents.document so the workflow
  appears in the kanban/list Actions menu (the Documents app has
  no regular form view to inherit from in v19)

The wizard:
- defaults to the company's first purchase journal
- supports vendor bill or vendor credit note
- copies the source attachment onto the new move
- posts a chatter note linking back
- marks the document linked so it stops appearing as a candidate

Auto-installs when documents + fusion_accounting_core are both
present. 8 unit tests cover the candidate flag, wizard happy path,
attachment copy, reverse linkage, already-linked guard, non-PDF
guard, and credit-note creation.

Made-with: Cursor

fusion_accounting_documents/views/account_move_views.xml

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="utf-8"?>
+<odoo>
+    <record id="view_move_form_inherit_fusion_documents" model="ir.ui.view">
+        <field name="name">account.move.form.inherit.fusion.documents</field>
+        <field name="model">account.move</field>
+        <field name="inherit_id" ref="account.view_move_form"/>
+        <field name="arch" type="xml">
+            <xpath expr="//div[@name='button_box']" position="inside">
+                <button class="oe_stat_button"
+                        type="object"
+                        name="action_open_source_documents"
+                        icon="fa-file-text-o"
+                        invisible="source_document_count == 0">
+                    <field name="source_document_count"
+                           widget="statinfo"
+                           string="Source Docs"/>
+                </button>
+            </xpath>
+        </field>
+    </record>
+</odoo>