chore(phoenix): decide and implement adapter package publishing posture

[christso]

Objective

Decide whether @agentv/phoenix-adapter stays private/repo-local or becomes publishable, then make release machinery match that decision.

Acceptance Signals

Private posture:

• Package remains private.
• Release and publish scripts intentionally omit the adapter.
• README and docs clearly document repo-local usage.

Publishable posture:

• Package metadata exposes the intended CLI/API surface.
• Release script updates the adapter version with other packages.
• Publish script includes the adapter only after build and package metadata are complete.
• Install smoke coverage imports the exported API and invokes CLI help without workspace-only paths.

Implementation Notes

Recommendation from the plan is to keep the adapter private until real AgentV execution and scorer parity are sufficient for a public contract.

Relevant files:

• packages/phoenix-adapter/package.json
• package.json
• scripts/release.ts
• scripts/publish.ts
• tsconfig.build.json
• .github/workflows/validate.yml
• packages/phoenix-adapter/README.md
• packages/phoenix-adapter/test/publish-smoke.test.ts

Non-goals

• Do not publish the adapter as an experimental half-state without release/install expectations documented.
• Do not add a public agentv phoenix CLI surface unless the public package contract is approved.