feat: add repo-local subminer workflow plugin

plugins/subminer-workflow/README.md

@@ -0,0 +1,49 @@
+<!-- read_when: migrating or using the repo-local SubMiner workflow plugin -->
+
+# SubMiner Workflow Plugin
+
+Status: active
+Last verified: 2026-03-26
+Owner: Kyle Yasuda
+Read when: using or updating the repo-local plugin that owns SubMiner agent workflow skills
+
+This plugin is the canonical source of truth for the SubMiner agent workflow packaging.
+
+## Contents
+
+- `skills/subminer-scrum-master/`
+  - backlog-first intake, planning, dispatch, and handoff workflow
+- `skills/subminer-change-verification/`
+  - cheap-first verification workflow plus helper scripts
+
+## Backlog MCP
+
+- This plugin assumes Backlog.md MCP is available in the host environment when the client exposes it.
+- Canonical backlog behavior remains:
+  - read `backlog://workflow/overview` when resources are available
+  - otherwise use the matching backlog tool overview
+- If backlog MCP is unavailable in the current session, fall back to direct repo-local `backlog/` edits and record that blocker in the task or handoff.
+
+## Compatibility
+
+- `.agents/skills/subminer-scrum-master/` is a compatibility shim that redirects to the plugin-owned skill.
+- `.agents/skills/subminer-change-verification/` is a compatibility shim.
+- `.agents/skills/subminer-change-verification/scripts/*.sh` remain as wrapper entrypoints so existing docs, backlog tasks, and shell history keep working.
+
+## Verification
+
+For plugin/doc/shim changes, prefer:
+
+```bash
+bun run test:docs:kb
+bash plugins/subminer-workflow/skills/subminer-change-verification/scripts/verify_subminer_change.sh --lane docs --lane core \
+  plugins/subminer-workflow \
+  .agents/skills/subminer-scrum-master/SKILL.md \
+  .agents/skills/subminer-change-verification/SKILL.md \
+  .agents/skills/subminer-change-verification/scripts/classify_subminer_diff.sh \
+  .agents/skills/subminer-change-verification/scripts/verify_subminer_change.sh \
+  .agents/plugins/marketplace.json \
+  docs/workflow/README.md \
+  docs/workflow/agent-plugins.md \
+  backlog/tasks/task-240\ -\ Migrate-SubMiner-agent-skills-into-a-repo-local-plugin-workflow.md
+```