docs: add phase 1 decision framework

docs/PHASE_1.md

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+# Phase 1
+
+## Purpose
+
+Phase 1 defines the technical decision-making framework that must be completed before implementation begins. This phase is about making and documenting core technical choices in a clear order so future work follows shared decisions rather than assumptions.
+
+## Scope
+
+Phase 1 establishes how technical and architectural decisions will be recorded, reviewed, and used to guide later implementation tasks.
+
+## In Scope
+
+- defining the major technical decisions required before implementation
+- documenting architecture decisions in a durable repository-owned form
+- establishing the relationship between architecture overview documents and ADRs
+- clarifying the minimum decision set required before implementation starts
+
+## Out of Scope
+
+Until the phase-1 decision framework is complete, do not:
+- start application implementation
+- introduce runtime services
+- choose implementation details that depend on unresolved architecture decisions
+- expand into feature delivery work
+- treat undocumented assumptions as approved decisions
+
+## Expected Outputs
+
+Phase 1 should produce:
+- a maintained phase-1 decision plan
+- a central architecture overview document
+- a set of ADRs covering major technical choices
+- clear implementation preconditions for the next phase
+
+## Decision Order
+
+Make decisions in this order:
+
+1. Define the required decision areas.
+2. Record the ADR process and naming conventions.
+3. Establish the architecture overview and its relationship to ADRs.
+4. Document major technical decisions in ADRs.
+5. Confirm that implementation-critical choices are explicit and aligned.
+
+## Exit Criteria for Phase 1
+
+Phase 1 is complete when:
+- the decision framework is documented
+- the architecture overview exists and points to ADRs
+- required major technical decisions are recorded as ADRs
+- implementation can begin without relying on undocumented assumptions