post-migration stale references: retired harness names in live docs and new code

[lann]

Sweep list from adversarial review (live docs that mislead; historical mentions excluded):

• AGENTS.md conformance layout block: still lists the deleted adapters/ (with the only layout mention of CONFORMANCE_BROWSER), report/, runner/, web/ ("serve with just conformance::web"), and root targets.toml alongside the -ct entries.
• AGENTS.md check-table row for the conformance suite: "gates on the wasmtime-rustcrypto and jco-node targets" — conformance-ct::all also always runs composed, and jco-browser in CI; the row omits matrix-update/matrix-check and CONFORMANCE_BROWSER. The two-target understatement is repeated later in the file.
• rust/guest-provider/README.md: "just conformance::class-d" — recipe is now conformance-ct::class-d.
• conformance/harness/src/lib.rs rustdoc: same stale recipe name.
• conformance/class-d/{oaep-encrypt,pss-sign,rsassa-sign}-probe/wit/world.wit: same stale recipe name — added post-migration by conformance: probe every withheld class-D interface, not two of five #297, i.e. the stale name is propagating into new code.
• conformance/{guest-ct,signing-guest-ct}/src/census-fixture.lock headers: "Generated by just conformance::update-lock; do not edit. The runner validates every results file against this inventory" — that recipe and runner are gone; the fixtures' actual role (frozen census anchors for census_test.rs) is not what the header says.
• .gitignore: dead patterns (conformance/adapters/jco/generated*, conformance/results/, conformance/matrix.md — the real matrices now live committed under driver-ct/).
• conformance/driver-ct/justfile: points at justfile.shared.just for the browser-predicate convention; shared.just now defines only the firefox/chromium predicates.

Related: #287 tracks pre-migration doc debt; this is a distinct post-#274 accumulation.