Append a ledger record

Requires a workspace-bound API key with ledger:write and an owner, admin, or member role. Appends one designator, observation, or claim. A designator with the same kind, namespace, and normalized value is reused (200, created false). Every claim cites at least one observation. The first line of a claim key supersedes nothing. Every later line, including a retraction, must supersede the current head, or the request fails with 409. Verification must be one the cited evidence supports: cross-linked and corroborated need retrievals of two different pages. Analytic means the only support is an analyst note. Other rule failures return 400 with the rule codes in detail. Send an Idempotency-Key header to make retries safe.