docs(arch): draft alknet-docker architecture specs (ADRs 058-063, OQs 048-051)

Greenfield architecture spec set for the alknet-docker crate — a thin,
single-host bollard wrapper exposing docker container/image operations
as call-protocol ops on the shared alknet/call ALPN, plus a
DockerTtyBackend (impl TtyBackend) behind a tty feature for interactive
terminal sessions into containers over alknet/tty.

Six ADRs:
- 058: docker ops on alknet/call (no separate ALPN; raw-carriage handoff
  dissolved by alknet-tty extraction — interactive attach moved to
  alknet/tty via DockerTtyBackend, no carriage field on call.requested)
- 059: bollard 0.21 (verified current on crates.io) + feature selection
  (http+pipe+time; no ssl/ssh/websocket/buildkit)
- 060: container resource model (ADR-050 application) — alknet.managed/
  alknet.owner labels, list owned_only flag, hosted-services operator
  role via static-resource fallback, handler-driven revoke with
  autonomous-death tolerance, resource-action vocabulary
- 061: DockerTtyBackend in alknet-docker behind tty feature (attach vs
  exec mode; POC drive_attach_raw as reference)
- 062: Docker client + OwnershipStore injection via closure capture
  (not Capabilities, not OperationContext — matches from_openapi pattern)
- 063: exit code on terminal call.responded for non-interactive exec
  (call.completed stays empty, ADR-012 unchanged)

Four spec docs (crates/docker/): README, overview, docker-operations,
docker-tty-backend. Four deferred-scope OQs (048-051): network/volume
ops, buildkit, system events subscription, create options surface.

Updates the tty-backend.md Backend implementations table (DockerTtyBackend
row now specced) and the architecture README (doc table, ADR table,
current-state paragraph, OQ count).

Grounded in the alknet-docker POC (docs/research/alknet-docker/poc-summary.md)
which validated the hard parts; the remaining lifecycle ops are mechanical
bollard wrapping. Reviewed by architecture-reviewer subagent; criticals
(the docker_client injection model conflicting with the Capabilities
contract) resolved via ADR-062/063 before commit.

docs/architecture/questions/049-image-build-buildkit-scope.md

@@ -0,0 +1,30 @@
+# OQ-49: Image Build (buildkit) Scope
+
+- **Origin**:
+  [crates/docker/docker-operations.md](crates/docker/docker-operations.md)
+  §"Out of scope for v1"; [ADR-059](decisions/059-bollard-021-dependency-and-features.md)
+  §3 (no `buildkit` feature).
+- **Status**: deferred(scope)
+- **Door type**: Two-way
+- **Priority**: low
+- **Blocked on**: a concrete use case for building images over the
+  call protocol. The two container use cases (disposable dev
+  containers, hosted services) pull pre-built images (`docker/image/pull`)
+  rather than building them. The reverse-proxy and other hosted
+  services build via `docker compose build` (operator-side), not via
+  alknet.
+- **Resolution**: Not yet decidable. bollard's `build_image` (image.rs:655)
+  and the `buildkit` feature (which pulls tonic +
+  bollard-buildkit-proto) are available but deferred. Build is a large
+  feature (build context upload, layer caching, multi-stage, buildkit
+  progress streaming) and is not needed for the current scope. When a
+  use case forces it, the operation is a `Subscription` (progress
+  events → `call.responded`, build complete → `call.completed`) and
+  the `buildkit` feature is enabled in `Cargo.toml` (two-way-door
+  feature addition, per ADR-059). The v1 surface has `image/pull` +
+  `image/list` + `image/inspect`; `image/build` is added when needed.
+- **Cross-references**:
+  [ADR-059](decisions/059-bollard-021-dependency-and-features.md)
+  (feature set decision — `buildkit` not enabled),
+  [crates/docker/overview.md](crates/docker/overview.md) §"bollard
+  version and features"