Landing page for `ai/tpt-backends/`: points at the contract spec
as required first reading, tables the 3 plans against their
issues/deps/size, and states the landing order + why.
Deats,
- TIPC first as the cheap proof the table-registration story
generalizes to a genuinely new proto (stdlib-only, and
`trio`'s sock wrappers are family-agnostic).
- `wg` layer-A next since it's deployable-today doc/example work.
- QUIC last, gated on its own prep PR.
- notes that plans 01 and 02 both want the same
`Address.rebind_from_sockname` gate, so whichever lands first
ships it.
(this patch was generated in some part by `claude-code` using `claude-opus-5` (`anthropic`))