chore(scaffold): initial SilverMetal program scaffold

Cross-platform privacy-hardening program. Two-layer product:
- SilverLABS Application Stack (cross-platform spine)
- Platform Hardening Profiles (per-OS, tier-honest)

Platforms: Linux (Debian/Kicksecure), Android (Pixel/Samsung/Moto/generic),
Windows (LTSC IoT), macOS (profile), iOS (MDM profile). Each flavour has
both a preflashed hardware SKU path and a self-apply "harden your existing
device" path.

Includes umbrella docs (README + threat-model, design-principles,
platform-matrix, roadmap, trust-model), per-platform and per-stack-
component README stubs, .gitignore, LICENSE.

Linux v1 ships first; Stack v1 = Browser + VPN + Sync.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

LICENSE

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+SilverMetal — Cross-Platform Privacy Hardening Program
+Copyright (c) 2026 SilverLABS
+
+This repository is a meta-project that integrates and configures multiple
+upstream open-source components, each carrying its own license. Components
+under this repository inherit the licenses of their upstream projects:
+
+  - linux/         — see component subdirectories; primarily GPLv2/v3 (Debian / Kicksecure)
+  - android/       — primarily Apache 2.0 (AOSP / GrapheneOS / LineageOS) and GPLv2 (kernel)
+  - windows/       — installer scripts and configurations: see SPDX headers
+  - macos/         — configuration profiles and scripts: see SPDX headers
+  - ios/           — configuration profiles: see SPDX headers
+  - stack/         — see component subdirectories; primarily AGPLv3 / MPL 2.0 / Apache 2.0
+
+Original SilverLABS-authored code in this repository (documentation,
+configuration overlays, build scripts, and integration glue) not derived
+from upstream components is licensed under the GNU Affero General Public
+License v3 (AGPL-3.0-or-later) unless an SPDX header in a specific file
+states otherwise.
+
+The full text of AGPL-3.0-or-later is available at:
+https://www.gnu.org/licenses/agpl-3.0.txt
+
+For per-component license details, see the README.md or LICENSE file in
+each subdirectory.