fix(addon): resolve all Odoo 18 install errors

- security/res_groups.xml: fully qualify ref('group_ai_user') with module prefix
- data/ir_cron.xml: remove numbercall field (removed in Odoo 17/18)
- views/menus.xml: remove web_icon referencing missing static/src/img/icon.png
- controllers/webhook.py: use get_json() instead of deprecated json.loads(data)
- security/ir.model.access.csv: use fully-qualified group external IDs (prior commit)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

addons/activeblue_ai/data/ir_cron.xml

@@ -8,7 +8,6 @@
             <field name="code">model.cron_ping_all()</field>
             <field name="interval_number">5</field>
             <field name="interval_type">minutes</field>
-            <field name="numbercall">-1</field>
             <field name="active">True</field>
         </record>
 
@@ -19,7 +18,6 @@
             <field name="code">model.sync_from_service()</field>
             <field name="interval_number">1</field>
             <field name="interval_type">hours</field>
-            <field name="numbercall">-1</field>
             <field name="active">True</field>
         </record>
 
@@ -30,7 +28,6 @@
             <field name="code">model.cron_cleanup_old()</field>
             <field name="interval_number">1</field>
             <field name="interval_type">days</field>
-            <field name="numbercall">-1</field>
             <field name="active">True</field>
         </record>
 
@@ -41,7 +38,6 @@
             <field name="code">model.cron_cleanup()</field>
             <field name="interval_number">1</field>
             <field name="interval_type">days</field>
-            <field name="numbercall">-1</field>
             <field name="active">True</field>
         </record>
     </data>