build: add checked Windows desktop archive packaging

docs/BUILDING.md

@@ -108,6 +108,32 @@ signing/notarization requires Apple tooling and credentials. See the
 
 ## CI and packaging gates
 
+### Windows archive for source installations
+
+After staging the CPU worker and media helpers, build an embedded-frontend
+desktop binary and collect its runtime files:
+
+```powershell
+Set-Location apps/desktop
+npm run tauri -- build --no-bundle
+Set-Location ../..
+python tools/package_windows.py
+```
+
+The generated `.searchi/packages/searchi-windows.zip` contains the desktop,
+matching-architecture Google worker, FFmpeg/FFprobe and notices. It excludes
+model caches, local settings and indexes. `PACKAGE.json` records SHA-256 for
+each included file. Extract the entire archive before launching `searchi.exe`.
+First launch uses normal verified model setup. WebView2 and the applicable
+Microsoft C++ runtime remain Windows prerequisites.
+
+This is an unsigned development archive, not a production installer. Native
+launch, clean-machine dependencies, upgrades and signatures must still be
+verified. The packager rejects mixed architectures and preserves a previous
+archive if validation fails. It does not certify GPU dependency packaging.
+
+### CI status and installer gates
+
 Gitea Actions are disabled for this repository at the owner's request after
 repeated failure emails (2026-10-12). Existing workflows remain as references:
 GitHub defines native OS matrices; Gitea targets its available Ubuntu runner.