CI: point NDI V_eta e2e at DID-matlab V2 (migrators merged via #151)

DID-matlab #151 merged the V_eta migrators to V2. The NDI V_eta e2e
workflows resolved DID_MATLAB_REF from github.head_ref (the shared topic
branch name), which still exists today but will break once that branch
is deleted. Default DID_MATLAB_REF to V2 (the migrators' durable home);
a workflow_dispatch input still overrides. This also re-validates the
cross-repo wiring against literal DID-matlab V2 -- the merge target.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BenWtpJyRu3QhEZqCErpwm

Author: claude

.github/workflows/test-eta-migrate-dab.yml

@@ -56,7 +56,10 @@ jobs:
     # so the ceiling is set well above the expected wall clock.
     timeout-minutes: 180
     env:
-      DID_MATLAB_REF: ${{ inputs.ref || github.head_ref || github.ref_name }}
+      # DID-matlab's V_eta migrators merged to V2 (#151, 2026-09-23); validate
+      # the cross-repo wiring against V2 so this resolves after the shared topic
+      # branch is deleted. A workflow_dispatch input still overrides.
+      DID_MATLAB_REF: ${{ inputs.ref || 'V2' }}
       # V_eta lives on did-schema `main` since #64 merged (2026-09-23) and the
       # shared topic branch was deleted; validate against main.
       DID_SCHEMA_REF: main

.github/workflows/test-eta-migrate-e2e.yml

@@ -73,7 +73,10 @@ jobs:
     name: V_eta second-pass end-to-end
     runs-on: ubuntu-latest
     env:
-      DID_MATLAB_REF: ${{ inputs.ref || github.head_ref || github.ref_name }}
+      # DID-matlab's V_eta migrators merged to V2 (#151, 2026-09-23); validate
+      # the cross-repo wiring against V2 so this resolves after the shared topic
+      # branch is deleted. A workflow_dispatch input still overrides.
+      DID_MATLAB_REF: ${{ inputs.ref || 'V2' }}
       # V_eta lives on did-schema `main` since #64 merged (2026-09-23) and the
       # shared topic branch was deleted; validate against main.
       DID_SCHEMA_REF: main

.github/workflows/test-eta-migrate-soph.yml

@@ -53,7 +53,10 @@ jobs:
     # pole; run 84 was still migrating at 2h41m when the shared job died.
     timeout-minutes: 350
     env:
-      DID_MATLAB_REF: ${{ inputs.ref || github.head_ref || github.ref_name }}
+      # DID-matlab's V_eta migrators merged to V2 (#151, 2026-09-23); validate
+      # the cross-repo wiring against V2 so this resolves after the shared topic
+      # branch is deleted. A workflow_dispatch input still overrides.
+      DID_MATLAB_REF: ${{ inputs.ref || 'V2' }}
       # V_eta lives on did-schema `main` since #64 merged (2026-09-23) and the
       # shared topic branch was deleted; validate against main.
       DID_SCHEMA_REF: main