feat(viewer): stream live pipeline GLBs into the browser viewport

Protocol: RunSnapshot gains CompletedSteps (accumulated from checkpoint
artifact paths, reset on start) so the frontend can tell when real
pipeline geometry exists. New coordinator method StepArtifact plus
GET /api/artifacts/steps serves steps/*.glb while a run is active (any
lifecycle status), traversal-guarded and .glb-only, so stages appear
without waiting for run completion.

Frontend: GLTFLoader loads the latest completed step into the viewport
group as soon as its checkpoint lands over SSE; replay placeholder
frames render only while no step artifacts exist. ?freeze=1 query param
stops rotation for deterministic screenshot verification. Three.js r160
and GLTFLoader (with BufferGeometryUtils) are vendored under public/
vendor with an import map and a window.THREE shim, replacing the CDN
UMD script; the ~1.4MB vendored three.js files are third-party
dependencies (MIT), not project assets.

Tests: store accumulation of completed artifact paths; steps endpoint
serves GLB during an active run, rejects traversal, 404s missing files.

Verified: dotnet build Debug+Release clean, 42/42 tests pass, Fable
compile clean, release server smoke serves index/vendor/steps endpoint.

1 files changed, 3 insertions, 2 deletions

diff --git a/public/SomhairlesDream.Shared/Artifact.js b/public/SomhairlesDream.Shared/Artifact.js
index 389d39c..6668abd 100644
--- a/public/SomhairlesDream.Shared/Artifact.js
+++ b/public/SomhairlesDream.Shared/Artifact.js
@@ -251,7 +251,7 @@ export function ArtifactManifest_$reflection() {
 }
 
 export class RunSnapshot extends Record {
-    constructor(ProjectId, RunId, BaseId, TargetId, Status, CurrentStepId, CurrentStepIndex, TotalSteps, LastHeartbeatAt, UpdatedAt, Message, ManifestPath, ManifestUrl, Error$, IsStale) {
+    constructor(ProjectId, RunId, BaseId, TargetId, Status, CurrentStepId, CurrentStepIndex, TotalSteps, CompletedSteps, LastHeartbeatAt, UpdatedAt, Message, ManifestPath, ManifestUrl, Error$, IsStale) {
         super();
         this.ProjectId = ProjectId;
         this.RunId = RunId;
@@ -261,6 +261,7 @@ export class RunSnapshot extends Record {
         this.CurrentStepId = CurrentStepId;
         this.CurrentStepIndex = (CurrentStepIndex | 0);
         this.TotalSteps = (TotalSteps | 0);
+        this.CompletedSteps = CompletedSteps;
         this.LastHeartbeatAt = LastHeartbeatAt;
         this.UpdatedAt = UpdatedAt;
         this.Message = Message;
@@ -272,6 +273,6 @@ export class RunSnapshot extends Record {
 }
 
 export function RunSnapshot_$reflection() {
-    return record_type("SomhairlesDream.Shared.RunSnapshot", [], RunSnapshot, () => [["ProjectId", string_type], ["RunId", string_type], ["BaseId", string_type], ["TargetId", string_type], ["Status", string_type], ["CurrentStepId", option_type(string_type)], ["CurrentStepIndex", int32_type], ["TotalSteps", int32_type], ["LastHeartbeatAt", option_type(class_type("System.DateTimeOffset"))], ["UpdatedAt", class_type("System.DateTimeOffset")], ["Message", string_type], ["ManifestPath", option_type(string_type)], ["ManifestUrl", option_type(string_type)], ["Error", option_type(string_type)], ["IsStale", bool_type]]);
+    return record_type("SomhairlesDream.Shared.RunSnapshot", [], RunSnapshot, () => [["ProjectId", string_type], ["RunId", string_type], ["BaseId", string_type], ["TargetId", string_type], ["Status", string_type], ["CurrentStepId", option_type(string_type)], ["CurrentStepIndex", int32_type], ["TotalSteps", int32_type], ["CompletedSteps", array_type(string_type)], ["LastHeartbeatAt", option_type(class_type("System.DateTimeOffset"))], ["UpdatedAt", class_type("System.DateTimeOffset")], ["Message", string_type], ["ManifestPath", option_type(string_type)], ["ManifestUrl", option_type(string_type)], ["Error", option_type(string_type)], ["IsStale", bool_type]]);
 }