feat(#918): loop.render-hooks resolver — consume the Capability Registry (ADR-857 phase 3c) (#920)

Add the loop.render-hooks resolver: the first registry-consuming query.
`gsd-tools loop render-hooks <point>` validates the point against the
authoritative canonical 12, reads the registry's materialized byLoopPoint
hooks, filters them by activation, and emits a JSON envelope {point,
activeHooks, rendered} with ordered markdown.

Activation resolves each hook's `when` key by precedence: loadConfig value
(post-cutover federated) -> raw config.json workstream/root single-key lookup
(pre-cutover central override) -> registry configSchema default (so a
default:true capability hook is active out-of-the-box) -> inactive. Guarded
single-value reads only (no merged object built from untrusted keys).

Registry-only: no workflow calls the resolver yet (wiring is the phase-6
cutover). Completes the phase-3 trio.

Closes #918

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

docs/ARCHITECTURE.md

@@ -372,6 +372,7 @@ Node.js CLI utility (`gsd-tools.cjs`) with domain modules split across `gsd-core
 | `profile-output.cjs`       | Profile rendering, USER-PROFILE.md and dev-preferences.md generation                                |
 | `loop-host-contract.cjs`   | Generated Loop Host Contract — 12 loop points, per-step agent roles, and core artifacts; emitted by `scripts/gen-loop-host-contract.cjs` from workflow markers (ADR-894 §3); consumed by `gen-capability-registry.cjs` |
 | `capability-registry.cjs`  | Generated central Capability Registry — role-partitioned index of all co-located capability declarations; emitted by `scripts/gen-capability-registry.cjs` (ADR-894 §5) |
+| `loop-resolver.cjs`        | Loop Extension Point resolver — ADR-857 phase 3c registry-consuming query; filters `byLoopPoint` by config activation, renders active hooks as markdown, emits `{ point, activeHooks, rendered }` envelope; `gsd-tools loop render-hooks <point>` |
 
 
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