Add first architecture decision record

docs/decisions/0001-initial-architecture.md

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+# ADR 0001: Initial Architecture Decisions
+
+**Date**: 2026-06-19
+**Status**: Accepted
+
+## Context
+
+We need a monitoring system for small water systems that is affordable, low-egress, and usable by both non-technical owners and professional operators.
+
+## Decision
+
+We will use a hybrid edge + cloud architecture with:
+- Raspberry Pi 5 edge devices
+- Tiered telemetry (compressed healthy summaries + rich alert payloads)
+- Monitored Objects as the core abstraction
+- Hybrid AI (small edge models + larger cloud models)
+- Multi-tenant web application with role-based access
+
+## Consequences
+
+- Strong emphasis on local processing to control data costs
+- More complex initial onboarding (AI interview + camera mapping)
+- Clear separation between Basic (owner) and Advanced (operator) dashboard views
+
+## Alternatives Considered
+
+- Pure cloud SCADA (too expensive for small systems)
+- Fully on-prem with no cloud (loses multi-system operator view and easier updates)