TypeSource interface

[Firehed]

Define Domain\TypeSource\TypeSource — the source-blind interface for resolving typed positions on symbols. Consumers hold this; no consumer sees whether an answer came from a native AST, a docblock, or reflection.

Interface takes symbol identity + which typed position:

• forFunctionReturn(FunctionName $fn): ?Type
• forMethodReturn(ClassName $class, MethodName $method): ?Type
• forParameter(ClassName|FunctionName $owner, ?MethodName $method, string $parameter): ?Type
• forProperty(ClassName $class, PropertyName $property): ?Type
• forConstant(ClassName $class, ConstantName $constant): ?Type

Additional for* methods may follow for AST-only positions (catch clauses, variable type-following). Not scope here.

No implementations, no wiring.

Done: src/Domain/TypeSource/TypeSource.php committed; method set covers every typed-declaration position current callers need (see sweep report on sweep/deprecated-factories).

---

Issue body drafted by AI; reviewed by human.