feat: publish monotonic identity catalog generations

[safal207]

Implements the monotonic publisher core for #643.

Adds an atomic publisher that observes governed identity timeline bundles and emits signed catalog generations without mutating agent identity data.

Core guarantees:

• generation numbers increase monotonically;
• an unchanged source set is restart-idempotent even when published_at changes;
• each changed generation references the previous publication digest;
• current and previous signing keys can co-sign during rotation;
• either rotation key can verify the transition generation;
• publisher state prevents replacing a newer generation with an older snapshot;
• an exclusive lock rejects concurrent publisher processes;
• history, current publication, compatible viewer catalog, and publisher state use atomic file replacement;
• interruption before current replacement never exposes a partial catalog;
• restart after an interrupted first publication safely recreates generation one;
• stale and invalid agents remain in the publication as non-authoritative;
• only VALID agents enter the compatible viewer catalog;
• per-agent visibility removes unauthorized agent IDs entirely.

Outputs:

• identity-catalog-publication.json;
• identity-catalog.json for the existing read-only viewer;
• identity-catalog-publisher-state.json;
• immutable history/generation-*.json snapshots.

Includes a production CLI with external JSON keyring and visibility configuration, a JSON Schema, crash-recovery tests, key-rotation tests, generation rollback tests, stale/invalid/visibility tests, and deterministic Python 3.9/3.11 CI.

Stack: #623 -> #626 -> #628 -> #629 -> #631 -> #633 -> #635 -> #639 -> #642 -> #645.

CI is green on Python 3.9 and 3.11, including Ruff, publisher tests, catalog/viewer regression, generation 1 publication, restart without duplication, dual-signed rotation into generation 2, governance regression, and Semgrep.

Evidence artifact: atomic-identity-catalog-publisher-evidence.
SHA-256: f4c00d01e614b9d6a1441270833a33fa524deb978393b0c4e4d76bbefa472053.

A follow-up will bind this publisher engine directly to the Trusted Runtime durable timeline commit hook.