feat: Phase 1 P1 — Dockerfile, AGNTCY alignment docs, Node.js SDK

Three remaining Phase 1 P1 deliverables:

1. Dockerfile — multi-stage build (builder + production), node:18-alpine,
   non-root USER node, .dockerignore excluding secrets and dev artifacts

2. AGNTCY alignment docs (docs/agntcy/) — README and alignment.md mapping
   all 6 AGNTCY domains to AgentIdP features with Phase 2/3 pending items noted

3. Node.js SDK (@sentryagent/idp-sdk) — TypeScript strict, zero any, native
   fetch (Node 18+), TokenManager with 60s auto-refresh, service clients for
   all 14 endpoints (agents, credentials, tokens, audit), AgentIdPError typed
   error hierarchy, full README

All three changes tracked under openspec/changes/ with tasks marked complete.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

openspec/changes/agntcy-alignment-docs/design.md

@@ -0,0 +1,13 @@
+## Context
+AGNTCY is the Linux Foundation open standard for AI agent identity, interoperability, and governance. AgentIdP implements the non-human identity model defined by AGNTCY. This document makes that alignment explicit and verifiable.
+
+## Goals
+- Engineers and architects can verify AGNTCY compliance without reading the full standard
+- The mapping is explicit: each AGNTCY concept is matched to a specific AgentIdP API feature
+- Both compliant and pending/out-of-scope items are documented honestly
+
+## Folder: docs/agntcy/
+Separate from developers/ and devops/ — this is a standards alignment reference, not a how-to guide.
+
+## Open Questions
+*(none)*