feat: migrate to runtime executeTask API

[foo-ogawa]

Background

agent-contracts-runtime v0.36.1 now provides high-level executeTask() and executeWorkflow() APIs that encapsulate the common boilerplate: adapter creation, DSL context loading, progress sink setup, and task/workflow invocation.

agent-contracts and artifact-contracts have already migrated to these APIs.

Current state

src/agents/orchestrator.ts contains:

• RUNTIME_PKG = ["agent-contracts", "runtime"].join("-") obfuscation pattern
• Local createAdapter(runtimePkg, name, config) switch with 4 adapter cases
• Manual runTask + createProgressSink wiring
• DSL registries loaded via dynamic import with silent empty fallback on failure
• esbuild plugin in esbuild.bundle.mjs that rewrites RUNTIME_PKG via regex

Required changes

1. Replace local createAdapter + runTask + createProgressSink with executeTask()
2. Remove RUNTIME_PKG variable and esbuild rewrite plugin
3. Use dsl: resolvedDsl (already available via static import from generated/dsl/dsl-data.js)
4. Replace silent empty fallback for DSL import failure with a proper error
5. Update agent-contracts-runtime devDependency to ^0.36.1

Reference implementation

See artifact-contracts PR #33 or agent-contracts PR #115 for the migration pattern.