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.
