refactor(work): drop date prefixes + move _state.json into _system/

Convention shift: epic folders + PRD filenames + frontmatter id
fields are now bare slugs. The created: timestamp (Phase 2) carries
the date; folder names don't repeat it. A future <task-id>-<slug>
shape (e.g. ClickUp) lands cleanly when that integration ships.

Renames (git mv preserves history):
- docs/work/2026-05-13-binder-wrap-helper/
    -> docs/work/binder-wrap-helper/
- docs/work/2026-05-14-library-evaluation-policy/
    -> docs/work/library-evaluation-policy/
- docs/work/2026-05-14-ci-security-and-supply-chain/
    -> docs/work/ci-security-and-supply-chain/
- docs/work/prds/2026-05-13-binder-wrap-helper.prd.md
    -> docs/work/prds/binder-wrap-helper.prd.md
- docs/work/prds/2026-05-13-coverage-architecture.prd.md
    -> docs/work/prds/coverage-architecture.prd.md
- docs/work/prds/2026-05-14-library-evaluation-policy.prd.md
    -> docs/work/prds/library-evaluation-policy.prd.md
- docs/work/prds/2026-05-14-ci-security-and-supply-chain.prd.md
    -> docs/work/prds/ci-security-and-supply-chain.prd.md

Frontmatter updates inside the renamed files: epic id, epic prd,
story epic, PRD id, PRD builds-on all drop date prefixes.

System folder + state file move:
- New docs/work/_system/ holds framework-managed state.
- docs/work/_state.json -> docs/work/_system/_state.json.
- state-builder.mjs adds _system to SKIP_FOLDERS.
- cli.mjs + state-sync-guard.mjs + .husky/pre-commit point at the
  new path.

template-reset-v1 epic deleted entirely (one-off cleanup epic from
the pre-date-convention era; status was already done).

Generator-template updates (so new artifacts ship in the right
shape):
- .sandcastle/decomposer.prompt.md emits bare-slug folder names +
  ISO created: timestamp.
- .claude/skills/to-prd/SKILL.md template uses bare-slug filename +
  bare-slug id field + ISO created: timestamp.

Doc reference updates: glossary, runbook, agent-first-workflow-
and-conformance, reviewer prompt, ADR-020, ADR-022, ADR-023 all
point at the new paths/slugs.

docs/work/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: 2026-05-14T19:16:52.691Z
+---
+
+## 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.