refactor: consolidate memory module with clear boundaries and extraction roadmap

[rollroyces]

Summary

Consolidates PilotDeck's memory subsystem with clear module boundaries and documents the path toward extracting the vendored edgeclaw-memory-core into a standalone npm package.

Changes

1. Barrel Exports (src/context/memory/index.ts)

Single entry point for all memory integration adapters:

• EdgeClawMemoryProvider and its option types
• createEdgeClawMemoryProviderFromConfig factory
• MemoryResolver interface and related types
• MemoryAttachmentBuilder class

2. Vendor README (src/context/memory/edgeclaw-memory-core/README.md)

Documents vendored library structure, build process, and internal architecture.

3. Extraction Roadmap (docs/memory-core-refactor.md)

Three-phase plan:

Phase	Status	Description
Phase 1	✅	Module boundary — barrel exports + README (this PR)
Phase 2	⏳	Extract to packages/edgeclaw-memory-core/ workspace package
Phase 3	⏳	Publish @openbmb/memory-core to npm

Architecture

PilotDeck Context Runtime
        │
        ▼
┌─────────────────────────┐
│  MemoryResolver (iface) │
│  EdgeClawMemoryProvider  │
│  MemoryAttachmentBuilder │
└─────────┬───────────────┘
          │ depends on
          ▼
┌─────────────────────────┐
│  edgeclaw-memory-core   │  ← vendored (~10 KLOC)
│  (service, retrieval,   │
│   storage, LLM extr.)   │
└─────────────────────────┘

Impact

• Cleaner import paths via barrel module
• Documented public API surface for future extraction
• Step-by-step migration plan for maintainers