ADR conventions

Decision

• Adopt docs/ADR/YYYY-MM-DD-NNN-<slug>.<lang>.md.
• Use lang values like ja / en, allowing future additions.
• Keep one file per decision per language.

Context

We needed a naming scheme that sorts chronologically and maps languages clearly.

Rationale

• Date and sequence together make chronology and decision number explicit.
• .<lang> makes the language explicit.
• Short slugs keep lists readable.

Consequences

Create paired ja and en files with the same date and sequence.