fix(a2ml): relocate campaign report under .machine_readable/

The a2ml-validate-action validator only matches TOML-form `name = "..."`
identity fields; this file uses s-expression form `(name "...")` so the
regex misses it and the validator reports "Missing required identity
field" even though the field is present.

The action has an explicit structural-identity exemption for files under
`.machine_readable/` — owning repo + path + filename carries identity
rather than an in-file key. This file is described in its own header
as "Estate sweep campaign report — machine-readable A2ML form", so
that's its natural home; the previous `docs/campaigns/` location was
the human-readable companion's directory.

No external references to the moved path (verified by repo-wide grep);
`.hypatia-ignore` entries point at sibling `.ts` triage files under
`docs/campaigns/2026-05-26/`, not the `.a2ml`.

Author: hyperpolymath