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/09-claude-md-update/_story.md

@@ -0,0 +1,39 @@
+---
+id: 09-claude-md-update
+epic: library-evaluation-policy
+title: CLAUDE.md Key Conventions — library policy bullet
+type: technical-story
+status: done
+feature: docs
+depends-on: [05-human-guide]
+blocks: []
+created: 2026-05-14T06:52:02+02:00
+updated: 2026-05-14T19:16:52.691Z
+---
+
+## Goal
+
+Add one bullet to the "Key Conventions" section of `CLAUDE.md` pointing agents and developers at ADR-022, the `evaluate-library` skill, and `docs/guides/adding-a-library.md`. No other changes to `CLAUDE.md`.
+
+## Why
+
+`CLAUDE.md` is the first file agents and developers read. Without a Key Conventions entry, the library evaluation policy is invisible to any agent starting a fresh session — it may run `pnpm add` without knowing the policy exists, and only hit the hook or pre-commit gate after the fact. The bullet closes the discoverability gap.
+
+## Done when
+
+- `CLAUDE.md` Key Conventions section contains a bullet: _"New runtime dependencies in feature- or core-tier packages require a library trace at `docs/library-decisions/<date>-<name>.md` produced by the `/evaluate-library` skill — see ADR-022 and `docs/guides/adding-a-library.md`."_ (exact wording may vary; substance must include ADR-022, the skill, and the guide path).
+- No other changes to `CLAUDE.md`.
+- `pnpm lint && pnpm fallow:audit` pass.
+
+## In scope
+
+- `CLAUDE.md` — one bullet in Key Conventions.
+
+## Out of scope
+
+- `docs/glossary.md` — the glossary entries for **Library trace** and **Pre-shipped trace** landed during the 2026-05-14 grill session and are already present.
+- Any other documentation changes.
+
+## Tasks
+
+- [x] Add the one-line library-policy bullet to CLAUDE.md Key Conventions (after confirming glossary entries are already present); all gates pass on this single commit.