docs: consolidate conditioning composition docs

Two documents described the conditioning composition layer:
docs/conditioning-layer.md (human-facing, linked from the
architecture entry point) and conditioning/ARCHITECTURE.md
(normative contract, cited from code comments). Both had
lagged the generator -- conditioning-layer.md by two campaigns
-- and they disagreed with each other: the live compose.ncl is
a three-segment law (core ++ modules ++ delta) over 19 roles in
three classes with a rendered constitution, while the docs still
described a two-segment, seven-role world.

Consolidate into docs/conditioning-layer.md, authored against
the live generator as ground truth: the three-segment law, the
producer/reviewer/council module classes, all 19 roles, the
single-sourced constitution render, and the real delivery
surfaces (output style + 18 agents + GEMINI.md). Delete the
redundant ARCHITECTURE.md, re-point its four code citations to
the surviving doc, and drop its vestigial campaign scaffolding
(per-node slot table, downstream-node checklist, reserved halts).

The generator itself was already correct; this is a docs-only
reconciliation. Verified: all 19 roles export, doc-audit link
gate passes, conditioning sweep 5/5.

Author: nrdxp