feat(ateapi): track actor_template_uid per snapshot on ExternalSnapshot

[shrutiyam-glitch]

Follow up on the comment - #1675 (comment)

Stamps actor_template_uid onto ExternalSnapshot so template provenance travels with the snapshot itself, rather than being inferred from the single ActorStatus.current_actor_template_uid.

Motivation

current_actor_template_uid records the template the last sprint booted with (finalizeRunning stamps it on every resume). It does not record the template the snapshot was captured under. Those two diverge as soon as an actor runs a sprint that does not produce a new durable snapshot, and loadActorForResume was using the former to decide whether to force a DATA-only restore instead of FULL.

Walking an actor through a repoint and a crash:

Step	Action	current_…_uid	ExternalSnapshot
a	Suspend on template A	A	captured on A
b	UpdateActor repoints the spec to B	A	captured on A
c	Resume → A != B, restores DATA, sprint boots on B	B	still on A
d	Actor crashes (or is reverted) — no new snapshot taken	B	still on A
e	Resume → current == target == B, so no repoint is detected	B	still on A

At step e the old check reports "template not replaced" and restores the external snapshot in FULL — replaying a memory image captured under A's sandbox on B. That is exactly the case the guard exists to prevent; it was silently defeated by the sprint at step c advancing current_actor_template_uid past the snapshot.

(Note: Paused actors do not face this divergence. Because UpdateActor is only allowed in the SUSPENDED state, a paused actor cannot have its template updated. Therefore, local checkpoints do not need separate template provenance tracking).

Changes

• Data Model Updates: Added the actor_template_uid field to ExternalSnapshot.
• Snapshot Stamping: Updated the capture logic to stamp external snapshots with the active sandbox's ActorTemplate UID when suspending an actor or creating an actor from a tag.
• Resume Evaluation Logic: Modified the external resume logic to compare the target template UID against the specific snapshot's UID (ExternalSnapshot.actor_template_uid) rather than the actor's overall status. Local restores bypass this check entirely since templates cannot change during a pause.

Tests

• TestResumeActor_AteletWireRequest (unit): snapshot fixtures now carry actor_template_uid, since provenance is read from the snapshot rather than from actor status.
• Functional expectations for create/update/resume/pause updated for the new field on the external snapshot golden files.
• TestUpdateTemplateLifecycle (e2e): asserts external_snapshot.actor_template_uid after suspend and re-suspend.

A TODO marks the resume → crash/revert → resume e2e sequence to be added once RevertActor lands — that is the path described in the table above.

• Tests pass
• Appropriate changes to documentation are included in the PR

[Zoe Zhao (zoez7)]

// Pause under template B while the external snapshot is still from
// template A: LocalSnapshotInfo records template B while ExternalSnapshot
// retains template A.

Is that true? After pause, the ExternalSnapshot entry should be cleared from the Actor.

[shrutiyam-glitch]

ensurePausedFinalized sets LocalSnapshotInfo and clears WorkerAssignment, leaving ExternalSnapshot intact.

[Zoe Zhao (zoez7)]

LocalTemplateReplaced should not be possible, updating an actor template is only allowed for suspended actors, this might be an existing bug.

[shrutiyam-glitch]

my bad, I went through the flow again, updating an actor's template is only possible in suspended state.
whenever an actor resumes from a local pause checkpoint (LocalSnapshotInfo != nil), its template could not have been changed via UpdateActor since the pause checkpoint was taken. So LocalTemplateReplaced is not required, removed and update the title and pr desc.