[FIX] contract: align Other Information tab into a single 2-col grid

The "Other Information" tab on the contract form had two outer
``<group>`` blocks. The first wrapped a single inner "Sales" group
(rendered on the left half, with the right half empty); the second
was a bare top-level ``<group>`` containing ``code``, ``group_id``
and ``currency_id`` -- which Odoo's form layout renders as a single
full-width column, so each of those fields was visibly wider than
the Sales group fields above and broke the visual rhythm of the
tab.

Merge them into one outer ``<group>`` with two inner groups
(``Sales`` + ``Administration``), so the whole tab renders as a
consistent 2-column grid and the second column lines up next to
the first.

No model change, no functional change -- pure layout fix.

Author: bosd

contract/views/contract.xml

@@ -363,14 +363,17 @@
                                         groups="base.group_multi_company"
                                     />
                                 </group>
-                            </group>
-                            <group>
-                                <field name="code" />
-                                <field name="group_id" />
-                                <field
-                                    name="currency_id"
-                                    groups="base.group_multi_currency"
-                                />
+                                <group
+                                    string="Administration"
+                                    name="group_administration"
+                                >
+                                    <field name="code" />
+                                    <field name="group_id" />
+                                    <field
+                                        name="currency_id"
+                                        groups="base.group_multi_currency"
+                                    />
+                                </group>
                             </group>
 
                             <group