Send runner capabilities with FetchTask poll

- Add envcheck import and capability detection to poller.go
- Send capabilities JSON with every FetchTask request
- Use GitCaddy actions-proto-go v0.5.6 with CapabilitiesJson field

go.sum

@@ -6,8 +6,8 @@ cyphar.com/go-pathrs v0.2.1 h1:9nx1vOgwVvX1mNBWDu93+vaceedpbsDqo+XuBGL40b8=
 cyphar.com/go-pathrs v0.2.1/go.mod h1:y8f1EMG7r+hCuFf/rXsKqMJrJAUoADZGNh5/vZPKcGc=
 dario.cat/mergo v1.0.0 h1:AGCNq9Evsj31mOgNPcLyXc+4PNABt905YmuqPYYpBWk=
 dario.cat/mergo v1.0.0/go.mod h1:uNxQE+84aUszobStD9th8a29P2fMDhsBdgRYvZOxGmk=
-git.marketally.com/gitcaddy/actions-proto-go v0.5.2 h1:+0tDJeyduhxpYrBNScN8w5din/0zJ/KtAh/Eo6mE9QE=
-git.marketally.com/gitcaddy/actions-proto-go v0.5.2/go.mod h1:mn7Wkqz6JbnTOHQpot3yDeHx+O5C9EGhMEE+htvHBas=
+git.marketally.com/gitcaddy/actions-proto-go v0.5.6 h1:G7T0vpx8HyCFWd0YMJ9sp8rCsWtzFrCJK4BMdOFJa1A=
+git.marketally.com/gitcaddy/actions-proto-go v0.5.6/go.mod h1:RPu21UoRD3zSAujoZR6LJwuVNa2uFRBveadslczCRfQ=
 gitea.com/gitea/act v0.261.7-0.20251202193638-5417d3ac6742 h1:ulcquQluJbmNASkh6ina70LvcHEa9eWYfQ+DeAZ0VEE=
 gitea.com/gitea/act v0.261.7-0.20251202193638-5417d3ac6742/go.mod h1:Pg5C9kQY1CEA3QjthjhlrqOC/QOT5NyWNjOjRHw23Ok=
 github.com/AdaLogics/go-fuzz-headers v0.0.0-20230811130428-ced1acdcaa24 h1:bvDV9vkmnHYOMsOr4WLk+Vo07yKIzd94sVoIqshQ4bU=