fix(templates): per-item branches for concept-stage nodes (was shared spec/auto-draft)

All 6 concept/idea-stage templates hardcoded the literal shared branch
spec/auto-draft instead of a per-item branch. Concurrent concept items
(now routine via the M41 auto-advance sweep) all pushed to the same
branch — a git collision risk. Switched to spec/${item.uuid}, matching
the established task/${item.uuid} convention used by every task-stage
template (merge@1, scaffold@1, etc — see spec/typed-workflows.md WF-COMP
stable-per-item-branch rationale). spec-review-loop@1's 4 nodes keep the
literal branch shared ACROSS the node set (now per-item, not global) so
loop iterations still accumulate on one branch per item, per spec's
cross-iteration-artifact caveat.

Files: review-spec-arch-opus@1.yaml, spec-draft-opus@1.yaml,
spec-review-loop@1.yaml, review-spec-arch-airouter@1.yaml,
spec-draft-airouter@2.yaml, scope-decompose-sonnet@1.yaml

task-templates/workflow/scope-decompose-sonnet@1.yaml

@@ -26,7 +26,7 @@ nodes:
     model: sonnet
     runtime_env:
       AGENT_REPO_URL: "git@gitea.oreillyit.nz-ai-enablement:skynet/agent-runtimes-agents.git"
-      AGENT_BRANCH: "spec/auto-draft"
+      AGENT_BRANCH: "spec/${item.uuid}"
       CP_URL: "http://controlplane.agent-runtimes.svc.cluster.local:8100"
       # AR-38: this stage's deliverable is work items POSTed to the CP, not a
       # repo diff — the empty-deliverable audit would fail every success.