Replace kebab-app's private `KEBAB_PARSE_MD_VERSION` literal with a
direct reference to `kebab_parse_md::PARSER_VERSION` so the parser
version cascade has a single source of truth (design §9 invariant).
Add maintenance comment on schema.rs WIRE_SCHEMAS const pointing to
docs/wire-schema/v1/ + kebab-cli wire helpers as the authoritative
sources to keep in sync.
Tighten open_existing doc comment to match the actual SQLITE_OPEN_READ_WRITE
flag (needed for WAL pragma application) — callers should still avoid
issuing mutations through this connection.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>