refactor(#1173): defer agents-kind descriptor declarations (option a)

Adopt maintainer-recommended option (a): keep the convertedAgentsKind /
stageAgentsForRuntimeWithConverter scope-threading plumbing, but DEFER the
8 runtimes' capability.json `agents`-kind declarations to a follow-up that
first ships the ADR-1235 §0 byte-for-byte parity harness.

The declarations were a live regression: the second `layout.kinds` consumer,
applySurface / `/gsd:surface` / `--materialize` (src/surface.cts), does not
mirror the legacy agent pipeline (copilot `.agent.md` rename, path-prefix
rewrite + attribution, stale cleanup), so a `/gsd:surface` toggle deleted
installed copilot `gsd-*.agent.md` and path-unrewrote the other 7 runtimes.
trek-e + davesienkowski both flagged this.

- Revert the agents-kind entries from the 8 capability.json files and
  regenerate capability-registry.cjs (now matches next; 0 converted agents
  kinds declared).
- Revert the declaration-driven kind-count test bumps
  (runtime-artifact-layout, descriptor-drive, bug-782, enh-789, enh-790).
- Keep the synthetic-descriptor seam tests for convertedAgentsKind dispatch;
  add a synthetic scope-threading test so the kept isGlobal plumbing stays
  covered without depending on real declarations.
- Update the convertedAgentsKind doc comment to state declarations are
  deferred pending the ADR-1235 §0 parity harness.
- Move ADR-1235 to Accepted.
- Reword the changeset to plumbing-only (docs-exempt now honest: no runtime
  declares the kind, legacy loop authoritative, installed output unchanged).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.changeset/clever-seals-rest.md

@@ -2,6 +2,6 @@
 type: Changed
 pr: 1438
 ---
-**Descriptor-driven install path now applies per-runtime agent conversion** for copilot/antigravity/cursor/windsurf/augment/trae/codebuddy/cline — their extracted agent converters (from #1099) are wired into the descriptor's `agents` kind, with install scope threaded for the scope-aware copilot/antigravity converters. Internal install-path parity step (ADR-1235 cutover); the legacy install loop remains authoritative so installed output is unchanged. (#1173)
+**Thread `isGlobal` install scope through the descriptor-driven `convertedAgentsKind` / `stageAgentsForRuntimeWithConverter` plumbing** — a prerequisite for the ADR-1235 agent-conversion cutover. No runtime declares a converted `agents` kind yet; the `capability.json` wiring is deferred to a follow-up that first ships the ADR-1235 §0 byte-for-byte parity harness (so the `/gsd:surface` / `--materialize` consumer can mirror the legacy agent pipeline before the kind goes live). The legacy `bin/install.js` agent loop remains authoritative, so installed agent output is unchanged. (#1173)
 
-<!-- docs-exempt: internal install-path wiring (ADR-1235 cutover); the legacy loop remains authoritative so installed agent output is unchanged — no user-facing command/config/behavior surface. -->
+<!-- docs-exempt: internal install-path plumbing only (ADR-1235 cutover prerequisite); no runtime declares the converted agents kind, the legacy loop remains authoritative, and installed agent output is unchanged — no user-facing command/config/behavior surface. -->