fix(langgraph-api): restore full message union in generated schemas

[Ali Tariq (valkrypton)]

langchain v1 made BaseMessage generic, which broke three assumptions in the static schema generator and left the messages channel as a degenerate oneOf: [RemoveMessage]. Studio matches this schema to detect messages graphs, so its Chat tab was greyed out for every v1 graph, including a vanilla MessagesAnnotation one.

• The inheritance map was keyed by a stringified base type. Generic subclasses keep their own type-param names in the extends clause while the one non-generic subclass gets the base's defaults substituted in, so RemoveMessage was the only member that matched at lookup time. Key on the base name with generic arguments erased. The erasure is not anchored on a trailing >, because long instantiations are already "..."-truncated by typeToString before they reach us.
• Only RemoveMessage is imported by value in the reducer code, so no other subclass declaration entered the per-graph program and the hierarchy walker never discovered them. Reference them in the template.
• Expanding those subclasses then hit $InferToolCalls<TStructure>, a deferred conditional type the generator cannot model, which aborted the whole schema. Leave such properties unconstrained instead, as already done for any/unknown.
• Emit the message definitions under bare names, since consumers match them by name. Limited to this hierarchy: erasing arguments globally collides (Record<string,any> and Record<string,string>), and those carried their arguments on v0 too.

Verified against a v0-line baseline: the messages ref and its union are now identical to what v0 emitted.

Fixes #2574

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Latest commit: 248854d

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This PR includes changesets to release 3 packages

Name	Type
@langchain/langgraph-api	Patch
@langchain/langgraph-cli	Patch
@langchain/langgraph-ui	Patch

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