docs(arch): decompose open-questions.md into per-OQ files under questions/

The monolithic open-questions.md (1310 lines, 47 OQs) was large enough to be
unmanageable, with high size variance (OQ-42 at 220 lines next to OQ-06 at 8).
Decomposed into one file per OQ under docs/architecture/questions/ (NNN-slug.md,
mirroring the ADR convention), with open-questions.md retained as the index:
theme-grouped tables plus a cross-theme Deferred/Blocked section that surfaces
the 6 deferred OQs with their Blocked-on conditions inline (the safe-exit
visibility surface). Per-OQ content moved verbatim; all 62 inbound links stay
valid (none used anchors). README's curated OQ summary dropped (now redundant
with the index tables).

Also seeds tasks/architecture/ with this task plus two follow-ups found during
the decompose: OQ-09/10 missing structured Blocked-on fields, and the
tasks/architecture/ blocker-task half of the Safe Exit protocol being
unenforced.

docs/architecture/questions/031-services-list-peers-re-export-semantics.md

@@ -0,0 +1,17 @@
+# OQ-31: services/list-peers Re-Export Semantics
+
+- **Origin**: [ADR-029](decisions/029-peer-graph-routing-model.md) §6, `docs/research/alknet-call-peer-routing/findings.md` §3.5
+- **Status**: **resolved** (2026-06-27)
+- **Door type**: Two-way
+- **Priority**: low
+- **Resolution**: `services/list` defaults to **"own ops only"** — it shows
+  the head's own Layer 0 `External` ops, filtered by
+  `AccessControl::check(calling_peer)`, unchanged from today (minus the
+  retired `remote_safe` filter). A `services/list-peers` opt-in (new
+  built-in operation) lists the peer overlays with attribution: each
+  peer's sub-overlay listed as `{ peer: Option<PeerId>, operations: [...] }`,
+  filtered by the calling peer's authorization. The re-export policy is an
+  `AccessControl` decision on the listing op. Whether `services/list-peers`
+  is built now or as a feature addition is a scheduling question — the
+  decision (opt-in, `AccessControl`-filtered) is made.
+- **Cross-references**: ADR-029, [client-and-adapters.md](crates/call/client-and-adapters.md)