docs(architecture): baseline current design (#109)

Capture the brownfield architecture and its relationship to the project vision.\n\n- add the current-state SAD and five retrospective ADRs\n- classify vision vectors against implementation evidence\n- record requirements, risks, gates, and construction handoff

.aiwg/architecture/adr-002.md

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+# ADR-002 — Keep the Reasoning Backbone Provider-Neutral
+
+**Status:** Accepted (retrospective)  
+**Date:** 2026-07-20
+
+## Context
+
+Users may use hosted APIs, local OpenAI-compatible servers, or already-authenticated coding-agent CLIs. No single provider supplies a stable universal capability contract.
+
+## Decision
+
+Resolve provider/model differences behind shared configuration and LLM/agent adapters. Treat provider responses as untrusted proposals; safety and tool contracts remain in T3MP3ST.
+
+## Consequences
+
+Users retain keyless/local options and provider choice. Compatibility and fallback testing expand, and lowest-common-denominator assumptions must not erase provider-specific behavior.