`#[serde(tag = "kind")]` rejects newtype variants whose payload is not a
struct, so 4 of 5 `Inline` variants (`Text(String)`, `Code(String)`,
`Strong(Vec<…>)`, `Emph(Vec<…>)`) failed to serialize at runtime — only
`Link { text, href }` worked. Convert every variant to struct form so the
internally-tagged shape is well-formed and round-trips through JSON.
Add `inline_serde_round_trip` covering all five variants. Per design §9,
this is a wire-schema migration; no `docs/wire-schema/v1/*.json` change
required since `Inline` is not directly referenced there. Callers in
kb-parse-md follow in the next commit.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
altair823
606ce1cf66