feat(openprd): revise standard to DIP-style numbered proposals (0.2) (#96)

Reshape OpenPRD from a private single-file (prd/<slug>/prd.md, gitignored) into a
published, numbered proposal collection like BIP/EIP/DIP: prd/NNNN-slug.md +
0000-template.md + a README index, committed to the repo, with a lifecycle
(Draft → Review → Accepted → Final; Rejected/Withdrawn/Superseded).

Tools (e.g. moshcode /prd) consume this to publish PRDs into whatever repo the
user is working in.

- docs/openprd.md — rewritten: numbering, lifecycle, directory layout, conformance.
- docs/openprd/0000-template.md — the canonical template.
- packages/schemas/schemas/openprd-prd.schema.json — 4-digit id, status enum,
  authors, discussion/implementation, supersedes/superseded-by.
- fixture updated to 0.2.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

packages/schemas/fixtures/openprd-prd.yaml

@@ -1,10 +1,12 @@
-openprd: "0.1"
-id: park-service-expansion
-title: Parked-domain service expansion
-status: draft
-owner: moshcoder.coinpay
+openprd: "0.2"
+id: "0001"
+title: Expand the parked-domain service
+status: Draft
+authors:
+  - anthony@profullstack.com
 repo: moshcoder/moshcoding
 created: 2026-07-12
+updated: 2026-07-12
 tags:
   - growth
   - monetization