Complete ORM core: _inherits, Related write-back, Copy, constraints

Batch 1 (quick-fixes):
- Field.Copy attribute + IsCopyable() method for copy control
- Constraints now run in Write() (was only Create — bug fix)
- Readonly fields silently skipped in Write()
- active_test: auto-filter archived records in Search()

Batch 2 (Related field write-back):
- preprocessRelatedWrites() follows FK chain and writes to target model
- Enables Settings page to edit company name/address/etc.
- Loop protection via _write_related_depth context counter

Batch 3 (_inherits delegation):
- SetupAllInherits() generates Related fields from parent models
- preprocessInheritsCreate() auto-creates parent records on Create
- Declared on res.users, res.company, product.product
- Called in LoadModules before compute setup

Batch 4 (Copy method):
- Recordset.Copy(defaults) with blacklist, IsCopyable check
- M2M re-linking, rec_name "(copy)" suffix
- Replaces simplified copy case in server dispatch

Batch 5 (Onchange compute):
- RunOnchangeComputes() triggers dependent computes on field change
- Virtual record (ID=-1) with client values in cache
- Integrated into onchange RPC handler

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

addons/product/models/product.go

@@ -131,6 +131,7 @@ func initProductProduct() {
 	m := orm.NewModel("product.product", orm.ModelOpts{
 		Description: "Product",
 		Order:       "default_code, name, id",
+		Inherits:    map[string]string{"product.template": "product_tmpl_id"},
 	})
 
 	m.AddFields(