Publish first signed Site Registry catalog trust

docs/PUBLIC_CATALOG.md

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+# Public signed catalog
+
+The v0.5.0 Forgejo release publishes the first immutable data generation that any
+Site Registry consumer can verify and resolve:
+
+- release: <https://git.argand.org/nicweyand/argand-site-registry/releases/tag/v0.5.0>
+- asset: `argand-site-registry-catalog-20260920-v1.tar.gz`
+- asset SHA-256:
+  `d878fa057397effa5dc729d2fa3a689c8edd1f4112ef1326dd6131b3fdeab63e`
+- generation pin:
+  `ede14746da8817aafdf705dd88cfeabbe8d23e1991e43a304acd8eca9249b18a`
+
+The release also carries a checksum file and an OpenSSH signature under namespace
+`argand-site-registry-release`. Verify it against
+[`trust/public-catalog-20260920/publisher-allowed-signers`](../trust/public-catalog-20260920/publisher-allowed-signers).
+The signed Git history is the independent channel for the trust root; do not learn
+the only trusted key from the archive it authenticates.
+
+```bash
+sha256sum --check argand-site-registry-catalog-20260920-v1.tar.gz.sha256
+ssh-keygen -Y verify \
+  -f trust/public-catalog-20260920/publisher-allowed-signers \
+  -I argand-site-registry-publisher-v1 \
+  -n argand-site-registry-release \
+  -s argand-site-registry-catalog-20260920-v1.tar.gz.sig \
+  < argand-site-registry-catalog-20260920-v1.tar.gz
+```
+
+After extraction, verify every member with `SHA256SUMS`, then authenticate the
+generation and exact reviewer trust root:
+
+```bash
+argand-site-registry activate \
+  --generation public-release-v0.5.0/catalog \
+  --current current.json \
+  --allowed-signers trust/public-catalog-20260920/publisher-allowed-signers \
+  --allowed-reviewers trust/public-catalog-20260920/reviewer-allowed-signers \
+  --identity argand-site-registry-publisher-v1
+
+argand-site-registry resolve \
+  --generation public-release-v0.5.0/catalog \
+  --pin ede14746da8817aafdf705dd88cfeabbe8d23e1991e43a304acd8eca9249b18a \
+  --query "yahoo mail"
+```
+
+## Scope and trust
+
+This first catalog is deliberately small. Its disclosed policy uses one automated
+evidence-gate reviewer group rather than claiming human-review quorum. Fresh exact
+endpoint observations are required, and source conflicts or dangerous drift need
+two groups, so the single automated reviewer must abstain on those risks. Sticky
+revocations and publisher/reviewer key separation remain enabled.
+
+Consumers decide whether this policy is appropriate for their use. Preserve typed
+abstentions, retain attribution, and apply independent malware and content policy.
+Do not route to the first raw lookup result. High-risk or disputed catalogs should
+use the unchanged two-human-reviewer reference policy.
+
+The generation's approvals expire. Installing an immutable archive is not a promise
+that every decision stays valid forever: use the resolver's requested time,
+consume cumulative signed revocation feeds when published, and move to a newly
+signed full generation before relying on renewed decisions.