0207 — binding.kind, header_match, and their CHECK constraint were dropped

Context. An earlier draft of the binding table carried a kind discriminator column, a header_match column, and a CHECK constraint tying them together, anticipating multiple matcher styles.

Decision. All three were dropped. With only one matcher style shipped (see 0206), the table is binding(consumer_group, pattern, display) — there is nothing to discriminate between.

Consequences. No speculative schema: if a second matcher style ever lands, the discriminator gets added when there are actually two things to tell apart, shaped by the real second case rather than a guess.