ci: TEMPORARY — run on engine-main pushes (dropped before main force-update)

The migrated history cannot open a PR against the stub main (no common
ancestor), so CI has no trigger on the proof branch. This commit only
adds engine-main to the push triggers; it is NOT part of the final
history — main will be force-updated to the parent commit (dc63226).

Author: softmarshmallow

.github/workflows/build-canvas.yml

@@ -5,6 +5,7 @@ on:
   push:
     branches:
       - main
+      - engine-main
   pull_request:
     paths:
       - ".github/workflows/**"

.github/workflows/check-generated-fbs.yml

@@ -30,6 +30,7 @@ on:
   push:
     branches:
       - main
+      - engine-main
   pull_request:
     paths:
       - "format/grida.fbs"

.github/workflows/test-crates.yml

@@ -4,6 +4,7 @@ on:
   push:
     branches:
       - main
+      - engine-main
   pull_request:
     paths:
       - ".github/workflows/**"