Record typed operator outcomes and exact-denomination combine

[hoffmang9]

Summary

• Add ADR 0027 for typed SignerError / Coinset / Dexie outcomes (no flatten-then-reparse).
• Record exact-denomination managed/CLI combine on ADR 0026, and restore missing ADRs in the index.
• Point operators at runbook §6 for greenfloord --once exit 1; keep combine examples at the YAML cap of 5.

Test plan

• Skim ADR 0026 vs 0027: combine policy is only in 0026; typed errors are only in 0027.
• Confirm runbook §6 documents --once fail-closed exit and exact-denom combine cap.
• Confirm README combine example uses --input-coin-count 5.