agent: command to list agent versions + resolvability (latest, all released, pinned, cached)

[AntoineToussaint]

Problem

There is no way to ask codefly "what versions of an agent exist, and which are actually usable?" Diagnosing module-saas-starter#3 required manually cross-checking, per agent: the pinned version, the git tags, and whether a downloadable release asset (or OCI manifest) actually exists — because a tag can exist with no published artifact. That inventory should be a first-class CLI command.

Ask

Add a command to list agent versions and their resolvability, e.g. codefly agent versions <publisher/name> and a broad codefly agent list.

For a single agent, show all known versions with a status per source:

codefly.dev/redis
  version   tag   github-release   oci(ghcr)   pinned-here   local-cache
  0.0.74    ✓     ✓ linux_amd64     -           ✓ (cache)     ✓
  0.0.73    ✓     ✗                 -                          ✓
  0.0.56    ✓     ✓                 -
  latest -> 0.0.74 (resolvable: yes)

Useful facets:

• latest published/resolvable version, and latest tag (may differ — that's the failure mode in impr: logger from context #3).
• which versions have a CI-downloadable artifact (GitHub release asset for the CI os/arch, and/or OCI manifest per AGENT_REGISTRY) vs. tag-only.
• the version pinned in the current workspace/module (from topology.bindings.codefly.yaml / service.codefly.yaml), flagged if it isn't resolvable.
• what's in the local cache (~/.codefly/agents/...), to make the local-vs-published gap obvious.
• --json for scripting.

Also consider a workspace-scoped codefly agent list that enumerates every agent pinned across the workspace with its resolvable/pinned/latest columns — a one-shot "are all my pins publishable?" view. Overlaps with the pre-flight validation in #101 (this is the interactive/inventory counterpart of that gate).

Tracking context: codefly-dev/module-saas-starter#3.