Push other-kind refs through bootstrap and add end-to-end coverage

Batched bootstrap previously errored on anything that wasn't a branch or create-only tag. Other-kind refs (refs/notes/, refs/pull/, custom namespaces enabled by AllRefs) need the same create-only path: rename the tag-phase to a tail phase and route both tags and other-kind plans through it. Tags still request include-tag in the fetch (IsTag=true); other-kind refs fetch by exact hash.

The integration test seeds refs/notes/commits on a source with two commits, runs an AllRefs sync into an empty target, and asserts the notes ref shows up at the expected hash. A second test pins the validator gate: mapping refs/notes/* without AllRefs errors out.