(2) class objects: bind `this` to the class-object value on static-method calls

[proggeramlug]

Part of #1785. Design: #1772. Depends on #1786.

(2) Static-method this-binding on class-object values

Problem

After #1786, a method call on a class-object value (const A = make(x); A.greet()) is resolved statically to the template at compile time, and the class_id vtable path passes this = undefined. So typeof this is undefined inside the static method and this.field (effect's annotations/pipe read this.ast) throws. Static methods also use a different this convention than instance methods on the dispatch path.

Scope

A method call whose receiver is a class-object value must dispatch dynamically and bind this to that value:

• HIR/codegen: a recv.method(...) where recv is a runtime value (not a statically-known class name) lowers to a dynamic method call passing recv as this — not a compile-time StaticMethodCall on the template.
• Runtime: the class_id dispatch path passes the receiver as this for static methods (reconcile the static-vs-instance this convention).
• this.field inside the static method resolves dynamically on the receiver (own field → prototype walk), not a compile-time static-field-get on the template.

Acceptance criteria

• function make(a){ return class { static ast=a; static viaThis(){ return this.ast } } } → make("X").viaThis() === "X", make("Y").viaThis() === "Y".
• typeof (make("X")).someStaticMethod === "function"; calling it sees this = the class object.
• No regression to static-method calls on top-level class declarations.

Blocks

(6).