Prune the ADRs aggressively

Question

Prune the ADRs, aggressively.

37 plugin ADRs plus 36 repo ADRs. tickets.md cites six of them in its first eight lines. Every ADR
is context a session pays for, and a superseded one is worse than absent: it is a wrong instruction an
agent will follow, and more ADRs mean more surface for hallucination.

Deleting lib/ reverses ADR-0018 (tested lib for deterministic IP), ADR-0021 (earns-its-place),
ADR-0031 (three-tier Method resolution), and narrows ADR-0023 §5. Record that once.

Then prune. Retire any ADR whose subject no longer exists — a deleted module, a retired Box, a
superseded decision. Superseded ADRs are removed, not archived: decision 15 is explicit that keeping
them is a source of conflict for agents. Decide nothing new here; this is deletion, not design.

Acceptance criteria

• One new ADR records the reversal of ADR-0018, ADR-0021 and ADR-0031 and the narrowing of
  ADR-0023 §5.
• Every ADR whose subject no longer exists is removed, and the index in the matching README.md
  matches what remains.
• No surviving ADR references a removed one.
• No new decision is introduced by this ticket.
• The remaining ADR count is stated, before and after.

Start with the ADR files and matching README.md index, then inspect tickets.md and the referenced decisions. Inventory subjects that no longer exist, including the deleted lib/ context, and verify surviving ADR references before and after removal. Done means the reversal is recorded, obsolete ADRs and references are removed, indexes match, and the before/after counts are stated.