chore(harness): drop superpowers plan/spec docs from the PR

These were brainstorming/spec artifacts not meant to ship; per review
feedback they don't belong in the foundation PR. Also de-references the
now-removed docs path in the harness-integration TODO comment.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: declan-scale

.github/workflows/harness-integration.yml

@@ -37,4 +37,4 @@ jobs:
     runs-on: ubuntu-latest
     if: false  # enabled once the first harness's test agents land
     steps:
-      - run: echo "populated by migration PRs"  # TODO(harness-migration): enable per-harness; see docs/superpowers/plans migration PRs 4-8
+      - run: echo "populated by migration PRs"  # TODO(harness-migration): enable per-harness; see migration PRs 4-8