chore: baseline container POC and atomic foundation plan

- Containerized Pi hello-world proof (image mosaic-poc-agent:0.84.4, non-root)
- Four immutable contract fixtures loaded into a generated system prompt
- build/hello/verify/reset scripts with exact-match gating and reset safety
- Documented Pi discovery (v0.84.4, -p mode, --system-prompt, container auth)
- Append-only BUILD-LOG with corrections; deferred layers in LAYERS.md
- Architecture plan: docs/plans/2026-09-02_atomic-mosaic-foundation.md

package.json

@@ -0,0 +1,10 @@
+{
+  "name": "mosaic-stack-dev-test",
+  "version": "0.1.0",
+  "private": true,
+  "description": "Minimal Mosaic Stack container proof of concept: one Pi agent, four local contract files, one real model request returning MOSAIC_HELLO_OK.",
+  "license": "UNLICENSED",
+  "dependencies": {
+    "@earendil-works/pi-coding-agent": "0.84.4"
+  }
+}