docs(architecture): record OQ-09 — slim-crate model under discussion

New open question capturing the doors-as-family-infrastructure
direction: alkssh (planned) becomes the ssh door for git, git is a
payload service exposed by downstream doors (alkhttp, alkssh, alknet),
and the crate set may slim to protocol crates + http adapter (kept in
alkgit, Slim-A, or promoted to an alkhttp git feature, Slim-B).

OQ-09 carries the three sub-decisions (alkgit-ssh deletion vs
temporary russh scaffolding; http adapter home; alkgitd consumption
path) and cross-references ADR-006 (now flagged as possibly superseded
before finalization) and OQ-01. Deferred summary table updated.

docs/architecture/decisions/006-http-adapter-composition.md

@@ -1,7 +1,9 @@
 # ADR-006: HTTP adapter composition — router factory in alkgit-http
 
 ## Status
-Proposed (recommendation recorded; final call pending user review — OQ-01)
+Proposed (recommendation recorded; final call pending user review — OQ-01,
+and now also OQ-09, whose slim-crate model may supersede this ADR's
+shape entirely)
 
 ## Context
 
@@ -84,8 +86,8 @@ hatch here is enough.
   reconciliation path).
 
 ## References
-- `docs/research/poc3-findings.md` §"alkhttp fit" (with_extra_routes surface), follow-up 1
+- `poc3-findings.md` §"alkhttp fit" (with_extra_routes surface), follow-up 1
 - `docs/research/vision.md` §"ALPN as a service", §"Sub-crate shape"
 - alkcall ADR-027 (precedent and its limits)
 - ADR-001 (crate decomposition), ADR-002 (session boundary), ADR-007/008/009
-- http.md, OQ-01, OQ-08
+- http.md, OQ-01, OQ-08, OQ-09 (may supersede this ADR)