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/01-trace-schema-extensions/_story.md

@@ -0,0 +1,51 @@
+---
+id: 01-trace-schema-extensions
+epic: ci-security-and-supply-chain
+title: Trace schema extensions (socketRisk + lastRevalidated)
+type: technical-story
+status: done
+feature: scripts
+depends-on: []
+blocks:
+  [
+    02-socket-integration,
+    04-major-bump-reevaluation,
+    05-trace-revalidation-workflow,
+  ]
+created: 2026-05-14T18:59:12+02:00
+updated: 2026-05-14T19:16:52.691Z
+---
+
+## Goal
+
+Extend `scripts/library-decisions/schema.mjs` with two new fields — `socketRisk` (the 9th filter result) and `lastRevalidated` (ISO-date or null) — and update `docs/library-decisions/_template.md` to reflect the expanded schema.
+
+## Why
+
+Every downstream enforcement layer (the evaluate-library skill's 9th filter, the check.mjs major-bump mode, the revalidate.mjs weekly cron) depends on these two fields being present and validated at the schema layer first. Landing them here in one green commit before any consumer touches them prevents schema-drift between layers.
+
+**External dependency:** library-evaluation epic story 01 (trace schema foundation) must be complete before this story — `scripts/library-decisions/schema.mjs` and `docs/library-decisions/_template.md` must exist. That epic is marked done.
+
+## Done when
+
+- `scripts/library-decisions/schema.mjs` exports an updated Zod schema where `filter-results` includes `socketRisk: z.union([z.literal("clean"), z.literal("flagged"), z.string()])` and the trace frontmatter includes `lastRevalidated: z.string().nullable()` (ISO date or null).
+- `docs/library-decisions/_template.md` mirrors both new fields with inline documentation of their allowed values.
+- `schema.test.mjs` covers: `socketRisk` round-trips for all three variants (`clean`, `flagged`, arbitrary string); `lastRevalidated` accepts ISO date strings and `null`; a trace missing `socketRisk` in `filter-results` fails validation; `lastRevalidated: null` is valid (default for fresh adoptions).
+- `pnpm typecheck && pnpm lint && pnpm test && pnpm conformance && pnpm fallow:audit && pnpm coverage:diff` all pass.
+
+## In scope
+
+- `scripts/library-decisions/schema.mjs` — schema additions only (no new exports, no breaking changes to existing field shapes).
+- `scripts/library-decisions/schema.test.mjs` — new test cases for the two new fields.
+- `docs/library-decisions/_template.md` — field documentation additions.
+
+## Out of scope
+
+- `socket-cli` invocation or Socket CI step — Story 02.
+- `check.mjs` major-bump mode — Story 04.
+- `revalidate.mjs` script — Story 05.
+- Backfilling existing traces with the new fields — Story 05 (the revalidation cron handles this on its first run).
+
+## Tasks
+
+- [x] Extend `scripts/library-decisions/schema.mjs` adding `socketRisk` (union: `"clean" | "flagged" | string`) to the `filter-results` Zod object and `lastRevalidated` (nullable ISO-date string) to the trace frontmatter schema; update `docs/library-decisions/_template.md` to document both fields with their enum values; add test cases to `schema.test.mjs` covering `socketRisk` round-trips (all three variants), `lastRevalidated` ISO + null acceptance, and missing-`socketRisk` rejection; all gates pass on this single commit.