Traces the version gap deferred by the alknet-blobs probe: verifies latest
stable iroh 1.0.2 / iroh-blobs 0.103 / irpc 0.17 against crates.io, rules out
the 'iroh 0.35 is a stale pin' hypothesis (it's load-bearing — 3 APIs broke),
identifies the real cheap win (irpc 0.16 is a dead dep in alknet-call, never
imported), and traces the iroh 1.0.x Preset trait so the migration is a
concrete 3-edit diff rather than a TODO.
Includes the sibling probe doc (alknet-blobs-external-store-probe.md) which
the findings cross-references.