Add all scaffolding, design, and decision documentation AKA first commit

tests/README.md

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+# Tests
+
+Cross-service integration and contract tests live here; unit tests live next to the code
+(`#[cfg(test)]` in Rust, `*.test.ts` for the frontend). The full plan is in
+[`../docs/06-test-strategy.md`](../docs/06-test-strategy.md).
+
+## Fixtures (`fixtures/`)
+- Short WAVs: 1-speaker, 2-speaker, overlap, silence, device-glitch (add binaries here; ignored
+  by git via `*.wav`).
+- `golden_transcript.json` — deterministic alignment/merge expectations.
+- Synthetic `.pst` (or a generator) with known events/attendees — never real mail data.
+- Recorded Ollama responses for offline LLM tests.
+
+## Cross-cutting gate
+The **privacy egress test** (FR-SEC-1) runs a representative flow under a network monitor and
+asserts no outbound connection except the configured local LLM endpoint and explicit model
+downloads. This gate blocks merge on failure — it is the product's most important guarantee.