feat: add persistent CPU search engine and CLI with lifecycle tests

docs/VALIDATION.md

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+# Validation evidence
+
+Development host: Windows VM, x86_64 MSVC, Rust stable 1.99.0.
+All local tests run on CPU; no GPU provider is configured.
+
+Initial foundation checks (2026-10-12):
+- `cargo test --workspace`: CLI parser/executable checks and engine retrieval,
+  lifecycle, exclusions, filters, migration and concurrent-reader checks passed.
+- `cargo clippy --workspace --all-targets -- -D warnings`: passed.
+- Rust formatting applied; final formatting verification follows integration.
+- Desktop TypeScript/Vite build passed; npm audit reported zero vulnerabilities.
+
+Not yet established: production latency targets, semantic inference, desktop
+runtime behavior, Linux/macOS execution, installer signing or upgrades.
+CI configuration is source configuration, not evidence that remote jobs ran.
+Gitea workflows require matching Windows, Linux and macOS runners; runner
+availability has not been established. GitHub workflows are also supplied for
+future mirroring, but do not run merely because code was pushed to Gitea.