Expand OpenManage AI documentation with architecture and deploy context.

Keeps runtime data and secrets out of git; documents relationship to OME Cockpit.

docs/ARCHITECTURE.md

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+# OpenManage AI architecture
+
+See root [README.md](../README.md) for the system diagram and relationship to OME Cockpit.
+
+## Components
+
+| Piece | Role |
+|-------|------|
+| Open WebUI | Chat UI, auth, model picker, tools |
+| vLLM | Inference backend |
+| ome_fleet tool | Reliable OME REST queries for demos |
+| OME MCP (optional) | Native tools — session stickiness unreliable in lab |
+
+## Data path for a tool-using question
+
+1. User selects **OME Copilot**
+2. Model emits tool call → Open WebUI executes `ome_fleet` / configured tools
+3. Tool hits OME REST (with SSL verify disabled for lab self-signed where configured)
+4. Model answers with concrete inventory facts