feat(capabilities): add claude-orchestration capability (Workflow backend) (#1143)

Default-off, BETA, claude-only capability adopting Claude Code's Workflow tool
(/effort ultracode, Agent SDK >= v0.3.149) as an optional parallel-execution
backend for the GSD loop. Restores the wave parallelism + plan-checker + verifier
that #853 forces inline on Claude Code, and folds gsd-ultraplan-phase under one
runtime gate.

- Pure fail-closed core (src/claude-orchestration.cts): detectWorkflowBackend
  (gate ladder: enabled -> Claude -> backend != inline -> nested+background host
  -> valid Agent SDK -> SDK >= floor; every miss degrades to inline) and
  emitWorkflowScript (waves -> parallel() barriers, plans -> gsd-executor +
  worktree, files_modified overlap -> separate stages, resumeFromRunId, budget).
  All interpolated identifiers validated script-safe; briefs JSON-quoted.
- claude-orchestration command family (gsd-tools claude-orchestration
  detect-backend|emit-workflow) for orchestrator invocation.
- Two gated loop contributions at wired points (execute:wave:post, plan:post);
  federated config keys (enabled/execution_backend/min_agent_sdk_version).
- ADR-1143 implementation amendment; CONTEXT.md glossary entry; explanation doc.

On any runtime lacking the Workflow tool, behaviour is byte-identical to today.

closes #1143

eslint.config.mjs

@@ -56,6 +56,8 @@ export default tseslint.config(
       'coverage/**',
       '**/*.generated.cjs',
       // ADR-457: tsc-generated runtime artifact — lint the src/*.cts source, not the emitted .cjs.
+      'gsd-core/bin/lib/claude-orchestration.cjs',
+      'gsd-core/bin/lib/claude-orchestration-command-router.cjs',
       'gsd-core/bin/lib/semver-compare.cjs',
       'gsd-core/bin/lib/host-integration.cjs',
       'gsd-core/bin/lib/handshake-serialized.cjs',