[TS Calls] Register and execute guarded semantic models

[CaelmBleidd]

Part of #360. Depends on #363 and P0 gate #383.

Goal

Select and execute a small set of guarded semantic models through the unknown-call dispatcher using the simplified contract.

Scope

• Keep one model object with a stable ID, declarative call target and execution producing guarded successors plus optional residual.
• Keep one immutable enabled-model catalog. Reject duplicate IDs and overlapping enabled targets; do not use registration order as priority.
• Match stable call metadata first, then check actual applicability against the state. A name or first possible receiver type is insufficient evidence of a built-in call.
• Return not-applicable when the whole call is unsupported. A returned plan handles supported inputs and routes its residual complement to the configured fallback.
• Preserve normal/exceptional completion, aliasing and deferred state changes on the selected successor.
• Document each model's supported domain and exactness within that domain. Do not require an EXACT/PARTIAL flag when residual presence already determines completeness of the returned plan.
• Use an intrinsic that actually benefits from an engine operation: migrate the existing Array.shift approximation using symbolic memory memcpy.
• Leave ordinary Array.pop source semantics to [TS Calls] Execute semantic models written in TypeScript #366.
• Use the observer from [TS Calls] Record unknown-call decisions #364. Compute outcomes from decisions; preserve one application event plus the separate residual decision.
• Preserve enabled-set identity for experiments. Tool revision and external source identity belong in run metadata; no per-model version scheme is needed.

Guard/model validation

Built-in models must define disjoint, exhaustive successor/residual guards and correct effects within their supported domain. Check these obligations in focused tests, with concrete TypeScript comparison where applicable. Do not perform an extra global solver-validation query on every model call.

Definition of Done

• [TS Calls][P0] Finish simplifying the model contract before further integration #383's simplification is present in the existing PR [TS Calls] Add guarded semantic models with a simplified contract #377; reuse the existing work.
• No separate descriptor/registration/backend/implementation wrapper stack or repeated implementation-kind values remain.
• Tests cover applicable and unsupported receivers, exact handling, guarded residuals, exceptions, mutation/aliases, deterministic catalog selection and ambiguous targets.
• Unknown/fake receivers never become ordinary object addresses merely to apply the model.
• Residual branches honor both configured policies.
• The catalog stays small; model-family expansion follows [TS Calls] Build a real-project call census and model roadmap #367/[TS Calls] Audit and classify existing semantic approximations #368.
• Relevant usvm-ts checks pass.

The gate can be satisfied in the same delivery as this issue; it does not require another implementation PR.