ADR-0000: Record architecture decisions

Status: accepted

Decisions that shape Vinxi are recorded as numbered ADRs in docs/adrs/, indexed by index.md (the single source of truth for what is live). One series, no parallel numbering. An ADR is immutable once accepted; changing course means a new ADR that names what it supersedes. Superseded ADRs stay in place with a status pointer — except era-scale resets, which move wholesale to docs/_archive/ (as the Reality-Kernel-era series 0000–0016 did; this series does not renumber against it and does not cite it as precedent). Vocabulary follows Naming.