Add initial project documentation

docs/architecture/overview.md

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+# Architecture Overview
+
+NexusAI is a modular, memory-centric AI system designed for persistent, context-aware conversations.  It separates concerns across different services that can be independently deployed and evolved
+
+## Core Design Principles
+- **Decoupled layers:** memory, inference, orchestration independent of eachother
+- **Hybrid retrieval:** semantic similarity (QDrant) combined with structured storage (SQLite) for flexible, ranked context assembly
+- **Home lab:**  Services are properly distributed across the various nodes according to available hardware and resources
+
+## Memory Model
+Memory is split between SQLite and QDrant, which both work together as a pair
+- **SQlite:** episodic interactions, entities, relationships, summaries
+- **QDrant:** vector embeddings for semantic similarity search
+
+When recallng memory, QDrant returns IDs and similarity scores, which are used to fetch full content from SQLite.  Neither SQlite or QDrant work in isolation
+
+## Hardware Layout
+|---|---|---|
+| Main PC | local | Primary inference (RTX A4000 16GB) |
+| Mini PC 1 | 192.168.0.81 | Memory service, Embedding service, Qdrant |
+| Mini PC 2 | 192.168.0.205 | Orchestration service, Gitea |
+
+## Service Communication
+All services expose a REST HTTP api.  The orchestration service is the single entgry-point.  Clients dont talk directly to the memory or inference services
+
+Client
+└─► Orchestration (:4000)
+├─► Memory Service (:3002)
+│     └─► Qdrant (:6333)
+│     └─► SQLite
+├─► Embedding Service (:3003)
+└─► Inference Service (:3001)
+└─► Ollama
+
+## Technology Choices
+| Concern | Choice | Reason |
+|---|---|---|
+| Language | Node.js (JavaScript) | Familiar stack, async I/O suits service architecture |
+| Package management | npm workspaces | Monorepo with shared code, no publishing needed |
+| Vector store | Qdrant | Mature, Docker-native, excellent Node.js client |
+| Relational store | SQLite (better-sqlite3) | Zero-ops, fast, sufficient for single-user |
+| LLM runtime | Ollama | Easiest local LLM management, serves embeddings too |
+| Version control | Gitea (self-hosted) | Code stays on local network |