docs: add phase 1 decision framework

docs/ARCHITECTURE.md

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+# Architecture
+
+## Purpose
+
+This document will become the central architecture overview for HoopScout v2. It should summarize the current approved technical direction and provide a stable starting point for future implementation work.
+
+## Current Status
+
+This is a phase-1 placeholder. The architecture is not yet fully defined, and implementation should not proceed from undocumented assumptions.
+
+## Decision-Driven Development
+
+Architecture in this repository should be decision-driven. Major technical choices should be documented before implementation begins, and implementation should follow documented decisions rather than informal local reasoning.
+
+## Relationship to ADRs
+
+This document should stay aligned with the ADR set in `docs/adr/`. ADRs capture specific decisions and their rationale. This overview should summarize the accepted decisions at a higher level, not replace the ADR record.
+
+## Future Sections Placeholder
+
+Future versions of this document may include sections such as:
+- system context
+- major components
+- data flow
+- deployment/runtime assumptions
+- integration boundaries
+- operational considerations