refactor(work): move epic folders into docs/work/epics/

The previous layout placed epic folders directly under docs/work/
alongside prds/ and _system/. Tightening: epics now live in their
own docs/work/epics/ subfolder, peer to prds/ and _system/. Same
shape as the existing prds/ bucket.

Final docs/work/ layout:
  README.md
  prds/<slug>.prd.md
  _system/_state.json
  epics/<slug>/_epic.md + <story-folder>/_story.md

Renames (git mv preserves history):
- docs/work/binder-wrap-helper/
    -> docs/work/epics/binder-wrap-helper/
- docs/work/library-evaluation-policy/
    -> docs/work/epics/library-evaluation-policy/
- docs/work/ci-security-and-supply-chain/
    -> docs/work/epics/ci-security-and-supply-chain/

Tooling updates:
- state-builder.mjs walks workRoot/epics/ directly; SKIP_FOLDERS
  obsoleted (no more sibling folders to filter out).
- dispatch.mjs's findNextTask, tickStoryBulletInEpic, and
  flipEpicDoneIfAllStoriesDone all join with "epics" segment.
- prd-ship.mjs's deriveShippingCommits walks workRoot/epics/ and
  git-logs docs/work/epics/<epic>/.
- decomposer.prompt.md emits epics under docs/work/epics/<epic-id>/.
- handoff + grill-with-docs glossary references updated.
- Glossary entry for Epic updated.

Reserved future shape: when a task-tracker integration (ClickUp,
Linear) ships, the epics/ subfolder hosts <task-id>-<slug>/
folders. Today it just hosts bare slugs.

docs/work/epics/ci-security-and-supply-chain/06-codeql-and-audit-signatures/_story.md

@@ -0,0 +1,42 @@
+---
+id: 06-codeql-and-audit-signatures
+epic: ci-security-and-supply-chain
+title: CodeQL workflow + pnpm audit signatures
+type: technical-story
+status: done
+feature: tooling
+depends-on: []
+blocks: [08-reviewer-prompt-update]
+created: 2026-05-14T18:59:12+02:00
+updated: 2026-05-14T19:21:52.308Z
+---
+
+## Goal
+
+Add two baseline GitHub-native gates: (1) a `pnpm audit signatures --audit-level=high` step in `ci.yml`'s validate job, and (2) a `.github/workflows/codeql.yml` workflow running javascript-typescript static analysis on push/PR/weekly schedule.
+
+## Why
+
+`pnpm audit signatures` catches tampered package signatures before they reach production — a post-install script from a compromised maintainer account would fail this check. CodeQL's javascript-typescript analysis catches common vulnerability patterns (XSS, injection, prototype pollution) that are invisible to dependency-scanning tools. Both are zero-cost on public repos and the GitHub Free plan; CodeQL's template includes a clear no-op on plans that don't support it.
+
+## Done when
+
+- `ci.yml`'s `validate` job includes a `pnpm audit signatures --audit-level=high` step. The step fails the job on `high` or `critical` severity signature failures.
+- `.github/workflows/codeql.yml` exists; triggers: `push: branches: [main]`, `pull_request`, and `schedule: - cron: "0 2 * * 3"` (Wednesday 02:00 UTC, staggered from the trace-revalidation cron); language: `javascript-typescript`; uses default queries. Includes a comment noting that CodeQL on private repos requires GitHub Advanced Security (consumer-toggleable per PRD constraint).
+- `pnpm typecheck && pnpm lint && pnpm test && pnpm conformance && pnpm fallow:audit && pnpm coverage:diff` all pass (no executable code change; CI config only).
+
+## In scope
+
+- `.github/workflows/ci.yml` — one new `pnpm audit signatures` step in `validate` job.
+- `.github/workflows/codeql.yml` — new workflow file.
+
+## Out of scope
+
+- Configuring GitHub branch protection to require CodeQL as a status check — consumer-facing instruction deferred to Story 09's guide.
+- OSSF Scorecard — explicitly out of PRD scope.
+- StepSecurity Harden Runner — explicitly out of PRD scope.
+
+## Tasks
+
+- [x] Add `pnpm audit signatures --audit-level=high` as a step in `ci.yml`'s `validate` job; one commit, all gates pass.
+- [x] Create `.github/workflows/codeql.yml` (language: `javascript-typescript`; triggers: push to main, pull_request, weekly schedule Wednesday 02:00 UTC; default queries; consumer note about GitHub Advanced Security requirement for private repos); one commit, all gates pass.