feat: add desktop document search and verified native CPU embeddings

docs/BUILDING.md

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+# Build and release targets
+
+Install stable Rust, Node 22+, and native Tauri development prerequisites.
+On Windows install Visual Studio C++ build tools and WebView2. Linux needs
+WebKitGTK 4.1 development libraries. macOS needs Xcode command-line tools.
+See https://v2.tauri.app/start/prerequisites/ for platform details.
+
+```powershell
+cargo test --workspace --locked
+cd apps/desktop
+npm ci
+npm run build
+# Windows VM: all rendering and inference tests must use CPU.
+$env:WEBVIEW2_ADDITIONAL_BROWSER_ARGUMENTS='--disable-gpu'
+npm run tauri -- dev
+```
+
+The desktop is a standalone Cargo workspace; validate it separately:
+
+```sh
+cargo test --manifest-path apps/desktop/src-tauri/Cargo.toml --locked
+```
+
+## Cross-compilation
+
+The Rust engine has no GUI dependency. Add the destination Rust target with
+`rustup target add TARGET`, then use `cargo build -p searchi-cli --target TARGET`.
+This requires the target linker, C toolchain and SDK because SQLite is compiled
+from bundled C. Target installation alone is insufficient. Document each
+verified host/target pair before treating it as supported.
+
+Desktop builds also need the platform webview libraries and packaging tools.
+Use native runners for dependable release builds. macOS signing/notarization
+needs Apple credentials and tooling. Windows installer cross-builds have
+additional Tauri caveats: https://v2.tauri.app/distribute/windows-installer/.
+
+## CI and packaging gates
+
+Both Gitea and GitHub workflow files are provided. Gitea needs registered runners
+matching the configured OS labels; this repository does not provision runners.
+No Linux/macOS checks are considered passed until actual job evidence exists.
+
+Current bundles are disabled during development. Enable installers only after
+packaging icons, native smoke tests, CPU model distribution and license review,
+upgrade/migration tests, signatures and rollback checks are ready. Do not place
+private signing keys, repository tokens or model credentials in source control.