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/library-evaluation-policy/04-evaluate-library-skill/_story.md

@@ -0,0 +1,48 @@
+---
+id: 04-evaluate-library-skill
+epic: library-evaluation-policy
+title: evaluate-library skill (SKILL.md + supporting files)
+type: technical-story
+status: done
+feature: tooling
+depends-on: [01-trace-schema-foundation]
+blocks: [05-human-guide]
+created: 2026-05-14T06:52:02+02:00
+updated: 2026-05-14T19:16:52.691Z
+---
+
+## Goal
+
+Create the `.claude/skills/evaluate-library/` directory with `SKILL.md` (the authoritative agent runbook), `POLICY.md` (ADR-022 mirror for quick reference), `TRACE-TEMPLATE.md` (showing the YAML frontmatter + heading shape the skill must emit), and an `EXAMPLES/` directory with two worked cases (one approved, one rejected). The skill must be invocable as `/evaluate-library <name> --tier <feature|core|app> --target <package-path>`.
+
+## Why
+
+Without a deterministic skill runbook, every agent evaluating a library does so ad hoc — different filters, different order, inconsistent trace format. The skill is the single source of truth for the 8-filter + 3-prompt sequence, the collect-cheap-skip-expensive ordering, and the trace write step. It also provides the canonical invocation the Claude hook emits.
+
+## Done when
+
+- `.claude/skills/evaluate-library/SKILL.md` exists and covers: invocation signature (`/evaluate-library <name> --tier <tier> --target <pkg-path>`), the 8 filters in collect-cheap-skip-expensive order (license, types, shadow-check, boundary-fit run to completion; maintenance, CVE scan, EU residency, named-consumer short-circuit after first reject), the 3 prompts, trace-write step (unconditional at evaluation end, including rejections), and the fail/skip sentinel for skipped expensive filters.
+- `.claude/skills/evaluate-library/POLICY.md` summarises ADR-022 in ≤2 pages — the filters, the tier trigger, the trace schema fields, the four enforcement layers.
+- `.claude/skills/evaluate-library/TRACE-TEMPLATE.md` shows the complete YAML frontmatter (all fields, real sentinel values for skipped filters) + all 11 required headings in order.
+- `.claude/skills/evaluate-library/EXAMPLES/` contains at least two worked trace files: one `decision: approved` trace and one `decision: rejected` trace (use `trpc-to-openapi` as the rejected example per the PRD, with `named-consumer: fail` and prose citing the grill-session conversation as provenance).
+- The skill is listed in `.claude/settings.json` (or wherever skills are registered) so `/evaluate-library` resolves to the SKILL.md via the Skill tool.
+- `pnpm lint && pnpm fallow:audit` pass.
+
+## In scope
+
+- `.claude/skills/evaluate-library/SKILL.md`
+- `.claude/skills/evaluate-library/POLICY.md`
+- `.claude/skills/evaluate-library/TRACE-TEMPLATE.md`
+- `.claude/skills/evaluate-library/EXAMPLES/approved-example.md`
+- `.claude/skills/evaluate-library/EXAMPLES/rejected-trpc-to-openapi.md`
+- Skill registration in `.claude/settings.json` (match existing skill registration pattern).
+
+## Out of scope
+
+- Automated tests for the skill (it is a prose runbook; correctness is verified by the success criterion in the PRD — running it against `trpc-to-openapi` produces the documented trace).
+- The schema module (Story 01) — already landed.
+- The human guide with worked examples for non-agent readers (Story 05).
+
+## Tasks
+
+- [x] Investigate the existing skill registration pattern (read `.claude/settings.json` and one existing skill's SKILL.md to confirm format and registration key); then write all five skill files (`SKILL.md`, `POLICY.md`, `TRACE-TEMPLATE.md`, `EXAMPLES/approved-example.md`, `EXAMPLES/rejected-trpc-to-openapi.md`) and register the skill; all gates pass on this single commit.