chore(aiwg): adopt shared BT6 maintainer workflow (#148)

* docs(policy): allow low-impact contributor courtesy cleanup

* chore(aiwg): migrate to shared BT6 maintainer plugin

* chore: reconcile delivery validation

.aiwg/plugins/bt6-maintainer/payload/capabilities/bt6-merge-train-flow.yaml

@@ -0,0 +1,66 @@
+apiVersion: ops.aiwg.io/v1
+kind: OpsCapability
+metadata:
+  name: bt6-merge-train-flow
+  labels:
+    category: maintainer
+    scope: cross-repository
+  annotations:
+    blast-radius: "repository-wide; merges one validated PR and may separately reconcile linked issues"
+spec:
+  description: Dry-run or execute an explicitly authorized BT6 merge train one verified PR at a time.
+  version: "0.2.0"
+  inputs:
+    - name: pr_numbers
+      type: list
+      required: true
+      description: Ordered candidates and audited head SHAs from a current queue audit.
+    - name: method
+      type: string
+      required: false
+      description: Merge method; must be permitted by authoritative project policy.
+    - name: dry_run
+      type: boolean
+      required: false
+      default: true
+      description: Report the planned train without merging when true.
+    - name: authorization
+      type: object
+      required: false
+      description: Current operator authorization for repository, candidates, method, and live mutation.
+  outputs:
+    - name: authorization_record
+      type: object
+      description: Resolved target, actor, scope, method, mode, and authority evidence.
+    - name: merged_prs
+      type: list
+      description: Merged PRs with exact SHA, method, checks, resulting commit, and linked-issue outcomes.
+    - name: stopped_before
+      type: list
+      description: Skipped or blocked candidates with exact stop reason.
+    - name: refreshed_queue
+      type: list
+      description: Base, CI, review, issue, dependency, and queue state after each merge or dry-run check.
+  target_requirements:
+    os: [linux, macos]
+    capabilities: [git]
+  agent: bt6-release-integrator
+  idempotent: false
+  steps:
+    - name: confirm-context-and-authorization
+      description: Require canonical repository/tracker resolution, current queue audit, expected actor, allowed method, and explicit live authorization.
+    - name: verify-one-candidate
+      description: Re-read exact head, base, mergeability, reviews, checks, dependencies, feedback, and risk-surface evidence.
+    - name: confirm-provider-assessment
+      description: For external-provider changes, require a current assessment with complete integration, claim traceability, and merge-ready exact-head gates.
+    - name: merge-one
+      description: Merge exactly one candidate only when dry_run is false and every gate passes.
+    - name: verify-result
+      description: Verify canonical-branch result and post-merge CI before any further action.
+    - name: reconcile
+      description: Observe linked-issue outcomes and mutate them only with separate explicit authorization.
+    - name: refresh
+      description: Refresh base, queue, checks, reviews, dependencies, and ordering before another candidate.
+  verification:
+    command: "git status --short --branch >/dev/null && git remote -v >/dev/null"
+    expect: "command exits 0 and live report includes explicit authorization plus tracker-derived merge evidence"