Backend improvements: views, fields_get, session, RPC stubs

- Improved auto-generated list/form/search views with priority fields,
  two-column form layout, statusbar widget, notebook for O2M fields
- Enhanced fields_get with currency_field, compute, related metadata
- Fixed session handling: handleSessionInfo/handleSessionCheck use real
  session from cookie instead of hardcoded values
- Added read_progress_bar and activity_format RPC stubs
- Improved bootstrap translations with lang_parameters
- Added "contacts" to session modules list

Server starts successfully: 14 modules, 93 models, 378 XML templates,
503 JS modules transpiled — all from local frontend/ directory.

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

pkg/orm/model.go

@@ -46,6 +46,7 @@ type Model struct {
 
 	// Hooks
 	BeforeCreate func(env *Environment, vals Values) error        // Called before INSERT
+	DefaultGet   func(env *Environment, fields []string) Values   // Dynamic defaults (e.g., from DB)
 	Constraints  []ConstraintFunc                                 // Validation constraints
 	Methods      map[string]MethodFunc                            // Named business methods
 
@@ -53,6 +54,11 @@ type Model struct {
 	computes      map[string]ComputeFunc // field_name → compute function
 	dependencyMap map[string][]string    // trigger_field → []computed_field_names
 
+	// Onchange handlers
+	// Maps field_name → handler that receives current vals and returns computed updates.
+	// Mirrors: @api.onchange in Odoo.
+	OnchangeHandlers map[string]func(env *Environment, vals Values) Values
+
 	// Resolved
 	parents    []*Model          // Resolved parent models from _inherit
 	allFields  map[string]*Field // Including fields from parents
@@ -227,6 +233,17 @@ func (m *Model) RegisterMethod(name string, fn MethodFunc) *Model {
 	return m
 }
 
+// RegisterOnchange registers an onchange handler for a field.
+// When the field changes on the client, the handler is called with the current
+// record values and returns computed field updates.
+// Mirrors: @api.onchange('field_name') in Odoo.
+func (m *Model) RegisterOnchange(fieldName string, handler func(env *Environment, vals Values) Values) {
+	if m.OnchangeHandlers == nil {
+		m.OnchangeHandlers = make(map[string]func(env *Environment, vals Values) Values)
+	}
+	m.OnchangeHandlers[fieldName] = handler
+}
+
 // Extend extends this model with additional fields (like _inherit in Odoo).
 // Mirrors: class MyModelExt(models.Model): _inherit = 'res.partner'
 func (m *Model) Extend(fields ...*Field) *Model {