fix(sqlite): commit local proofs with their operations

[marcus-pousette]

Problem

If a local operation commits and its authorization proof is stored afterward, a crash between those writes leaves an operation that cannot be safely forwarded or audited.

What changes

Every optimistic SQLite commit requires a 64-byte signature and 16-byte proof reference. The native extension writes that complete proof into treecrdt_sync_op_auth inside the same savepoint as the operation, materialized tree changes, and materialization metadata.

Both schema initialization orders enforce NOT NULL, length(sig) = 64, and length(proof_ref) = 16. The operation reference comes from the operation actually committed and the database clock supplies the timestamp.

Clean-slate choice

There is no proofless commit arity, optional reference, unconstrained old schema, migration, or durable mirror. Authenticated optimistic commits are proof-bearing by contract. Unauthenticated writes use #193's separate immediate path.

Fast paths

• The immediate unauthenticated UDF performs no sidecar write.
• The proof store reads the native row directly.
• The authenticated commit adds one co-transactional row, with no second transaction or lookup.

Failure behavior

Any bind, constraint, insert, trigger, finalization, materialization, or savepoint-release failure rolls back operation, proof, tree state, and metadata together.

Verification

• SQLite extension: 26/26
• malformed/missing/wrong-width proof rejection
• both schema initialization orders
• op-ref derivation, database timestamps, and atomic rollback

Stack

Stacked on #193 and consumes #187's exact-proof shape.