feat(kfd): group provider tools under eks (back-compatible)

[nutellinoit]

Summary 💡

Groups the kfd.yaml tools per provider: opentofu and furyagent are now pinned under
tools.eks (they are EKS-only). The change is backward compatible — the model still accepts
the previous layout (these tools, and the legacy terraform, under tools.common), so older
distributions keep working with a furyctl that reads the new location first.

Related furyctl PR: sighupio/furyctl#672
Pre-release tag for furyctl to consume: v1.34.2-rc.3

Description 📝

• kfd.yaml: opentofu and furyagent moved under tools.eks (next to awscli); tools.common
  keeps the truly common tools (kubectl, kustomize, yq, helm, helmfile, kapp).
• pkg/apis/config/model.go: KFDToolsEks gains optional opentofu/furyagent. KFDToolsCommon
  keeps opentofu/furyagent/terraform as optional (no longer required) for backward
  compatibility with distributions < 1.34.2. model.go is hand-written, no regeneration.

Breaking Changes 💔

None. The model is additive: new distributions pin under tools.eks, older ones keep tools.common,
and furyctl resolves provider-first with a common fallback (see related PR). Requires the
v1.34.2-rc.3 pre-release for furyctl.

Tests performed 🧪

• go build ./...
• furyctl (split-tools) consumes v1.34.2-rc.3: EKS reads tools from tools.eks; OnPremises
  gets only the common tools (new layout) and still resolves opentofu/furyagent from tools.common
  on older distributions (cold-cache e2e against v1.34.1)
• bump furyctl with an rc version to make CI green again (after the PR from furyctl is approved)