Complete ORM gaps + server features + module depth push

ORM:
- SQL Constraints support (Model.AddSQLConstraint, applied in InitDatabase)
- Translatable field Read (ir_translation lookup for non-en_US)
- active_test filter in SearchCount + ReadGroup (consistency with Search)
- Environment.Ref() improved (format validation, parameterized query)

Server:
- /web/action/run endpoint (server action execution stub)
- /web/model/get_definitions (field metadata for multiple models)
- Binary field serving rewritten: reads from DB, falls back to SVG
  with record initial (fixes avatar/logo rendering)

Business modules deepened:
- Account: action_post validation (partner, lines), sequence numbering
  (JOURNAL/YYYY/NNNN), action_register_payment, remove_move_reconcile
- Sale: action_cancel, action_draft, action_view_invoice
- Purchase: button_draft
- Stock: action_cancel on picking
- CRM: action_set_won_rainbowman, convert_opportunity
- HR: hr.contract model (employee, wage, dates, state)
- Project: action_blocked, task stage seed data

Views:
- Cancel/Reset buttons in sale.form header
- Register Payment button in invoice.form (visible when posted+unpaid)

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

pkg/orm/model.go

@@ -50,6 +50,9 @@ type Model struct {
 	Constraints  []ConstraintFunc                                 // Validation constraints
 	Methods      map[string]MethodFunc                            // Named business methods
 
+	// SQL-level constraints
+	SQLConstraints []SQLConstraint
+
 	// Computed fields
 	computes      map[string]ComputeFunc // field_name → compute function
 	dependencyMap map[string][]string    // trigger_field → []computed_field_names
@@ -216,6 +219,19 @@ func (m *Model) IsAbstract() bool { return m.modelType == ModelAbstract }
 // IsTransient returns true if this is a wizard/temporary model.
 func (m *Model) IsTransient() bool { return m.modelType == ModelTransient }
 
+// SQLConstraint represents a SQL-level constraint on a model's table.
+// Mirrors: _sql_constraints in Odoo.
+type SQLConstraint struct {
+	Name       string // Constraint name
+	Definition string // SQL definition (e.g., "UNIQUE(name, company_id)")
+	Message    string // Error message
+}
+
+// AddSQLConstraint registers a SQL-level constraint on this model.
+func (m *Model) AddSQLConstraint(name, definition, message string) {
+	m.SQLConstraints = append(m.SQLConstraints, SQLConstraint{Name: name, Definition: definition, Message: message})
+}
+
 // ConstraintFunc validates a recordset. Returns error if constraint violated.
 // Mirrors: @api.constrains in Odoo.
 type ConstraintFunc func(rs *Recordset) error