[ADD] inventory: Improve stock info and UI in product form

Before:
Users could easily get confused or make mistakes when managing stock,
especially in multi-company environments. Important actions like
updating quantity on hand were hard to find, and the interface didn’t clearly
guide safe workflows.

After:
The interface now better supports new users by reducing confusion and
make stock workflows safer. Risky actions are hidden if not appropriate, visual
clarity helps users avoid errors and understand inventory status more easily.

task-4965098

Author: arkp-odoo

quantity_on_hand/__init__.py

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+# Part of Odoo. See LICENSE file for full copyright and licensing details.
+
+from . import models

quantity_on_hand/__manifest__.py

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+# Part of Odoo. See LICENSE file for full copyright and licensing details.
+
+{
+    'name': 'Quantity on hand',
+    'version': '1.0',
+    'depends': ['stock'],
+    'installable': True,
+    'author': 'arkp',
+    'data': [
+        'views/product_template_views.xml',
+    ],
+    'license': 'LGPL-3',
+}

quantity_on_hand/models/__init__.py

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+# Part of Odoo. See LICENSE file for full copyright and licensing details.
+
+from . import product_template

quantity_on_hand/models/product_template.py

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+# Part of Odoo. See LICENSE file for full copyright and licensing details.
+
+from odoo import api, fields, models
+
+
+class ProductTemplate(models.Model):
+    _inherit = 'product.template'
+
+    is_multilocation = fields.Boolean(compute="_compute_is_multilocation")
+
+    @api.depends('product_variant_ids.stock_quant_ids.location_id')
+    def _compute_is_multilocation(self):
+        for record in self:
+            internal_location_ids = {
+                loc.id
+                for loc in record.mapped(
+                    'product_variant_ids.stock_quant_ids.location_id'
+                )
+                if loc.usage == 'internal'
+            }
+            record.is_multilocation = len(internal_location_ids) > 1

quantity_on_hand/views/product_template_views.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<odoo>
+    <record id="view_product_template_form_inherited" model="ir.ui.view">
+        <field name="name">product.template.form.custom.inherit</field>
+        <field name="model">product.template</field>
+        <field name="inherit_id" ref="product.product_template_only_form_view" />
+        <field name="arch" type="xml">
+
+            <xpath expr="//button[@name='action_update_quantity_on_hand']" position="attributes">
+                <attribute name="invisible">1</attribute>
+            </xpath>
+
+            <xpath expr="//button[@invisible='not show_on_hand_qty_status_button']"
+                position="attributes">
+                <attribute name="invisible">1</attribute>
+            </xpath>
+
+            <xpath expr="//field[@name='virtual_available']"
+                position='attributes'>
+                <attribute name='decoration-danger'>virtual_available &lt; 0</attribute>
+                <attribute name='decoration-primary'>virtual_available == 0</attribute>
+            </xpath>
+
+            <xpath
+                expr="//button[@name='action_product_tmpl_forecast_report']/div/span[hasclass('o_stat_value', 'd-flex', 'gap-1')]/field[@name='uom_name']"
+                position='replace'>
+                <span>Forecasted</span>
+            </xpath>
+
+            <xpath
+                expr="//button[@name='action_product_tmpl_forecast_report']/div/span[hasclass('o_stat_value', 'd-flex', 'gap-1')]"
+                position='before'>
+                <span class="o_stat_value d-flex gap-1">
+                    <field name="qty_available" nolabel="1" class="oe_inline" />
+                    <field name="uom_name" class="oe_inline" />
+                </span>
+            </xpath>
+
+            <xpath
+                expr="//button[@name='action_product_tmpl_forecast_report']/div/span[hasclass('o_stat_text')]"
+                position='attributes'>
+                <attribute name='invisible'>1</attribute>
+            </xpath>
+
+        </field>
+    </record>
+
+    <record id="product_template_form_view_inherit" model="ir.ui.view">
+        <field name="name">product.template.common.form.inherit</field>
+        <field name="model">product.template</field>
+        <field name="inherit_id" ref="product.product_template_form_view" />
+        <field name="arch" type="xml">
+
+            <xpath expr="//field[@name='product_tooltip']" position='attributes'>
+                <attribute name='invisible'>type == 'consu'</attribute>
+            </xpath>
+
+            <xpath expr="//field[@name='product_tooltip']" position="after">
+                <label for="qty_available" invisible='not is_storable'>Quantity On Hand</label>
+                <span class="d-flex gap-3">
+                    <field name="qty_available"
+                        readonly="is_multilocation"
+                        class="oe_inline"
+                        invisible='not is_storable'
+                    />
+                    <field name="uom_name" class="oe_inline" invisible='not is_storable' />
+                    <button type="action"
+                        name="%(stock.action_product_stock_view)d"
+                        class="oe_stat_button oe_inline opacity-0 opacity-100-hover"
+                        invisible="not is_storable">
+                        Update
+                    </button>
+                </span>
+            </xpath>
+
+        </field>
+    </record>
+</odoo>