ci: route main gates to general and AI runners

[Daliys]

Summary

Aligns the NexusUnity main branch with the shared CI runner contract.

Changes

• Routes Code Linter, Python Quality Gate, and Unity Quality Gate to Default + ci-scope.
• Routes Slop Review to Default + ci-scope-ai with Ollama model qwen3-coder:30b-a3b-q4_K_M.
• Routes the in-repository Documentation quality AI job to ci-scope-ai.
• Gives the two AI jobs the shared non-cancelling ci-scope-slop-review concurrency group.
• Leaves the isolated V2 canary workflow unchanged.

Validation

• Workflow YAML parsed successfully.
• git diff --check
• This release-style PR targets main from the required ci-scope/* branch.