Not-found lookups return null; parallelizes fallback resolution

Patch Changes

• 1e617b8: Soften the not-found UX for read-only lookups (releases get, releases release get) and parallelize releases get fallback resolution.

  A miss on releases get <thing> is a normal answer for a lookup, not a software fault. The output now reads [releases] No <kind> matching: <input> (info-level, no red ERROR: framing). In --json mode the command also writes null to stdout before the stderr line, so JSON consumers get parseable output instead of nothing. Exit code stays 1 — the contract for "scripts can detect a miss" doesn't change.

  When the identifier doesn't carry a typed-ID prefix, releases get previously made up to three sequential API round-trips (findOrg → findProduct → findSource) before giving up. Those now run in parallel via Promise.all, so a miss takes ~one round-trip instead of three. Hits behave the same — the first matching kind wins.

  Mutating commands (release delete/update/suppress/unsuppress, delete, update, ignore add/remove, product alias, etc.) keep the louder error treatment; for those, "thing doesn't exist" really is an error.