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>

macos/README.md

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+# SilverMetal macOS
+
+**Status**: Phase 4 (planning, post-Windows v1)
+
+Tier C-D — signed configuration profile + setup script + Stack ports. We cannot modify macOS; we configure everything Apple exposes.
+
+## Scope (v1)
+
+- Signed `.mobileconfig` profile that:
+  - Enforces FileVault
+  - Disables analytics, Siri uploads, advertising identifiers
+  - Configures application firewall
+  - Restricts iCloud to absolute minimum
+  - Enables Lockdown Mode (per-user opt-in guidance)
+- Idempotent setup script for non-MDM hardening (default-app changes, Safari→SilverBrowser, etc.)
+- Stack ports for macOS (universal binaries, notarised, signed)
+- Setup guide for hardware-key 2FA, anti-forensics
+
+## Out of scope
+
+- Anything requiring kernel extension or system extension privileges beyond what Apple sanctions
+- Anything that disables SIP / Gatekeeper (we keep both ON)
+- Anything that requires bypassing Apple's signing chain
+
+## Directory layout
+
+To be populated in Phase 4:
+
+```
+macos/
+├── profile/         # .mobileconfig sources, signing
+├── setup/           # idempotent setup script
+├── stack-installer/ # native macOS Stack package builders (.pkg)
+└── docs/            # setup guide, recommended apps
+```
+
+## Verification gates
+
+- Profile signature verifies under Apple's signing chain
+- FileVault confirmed enabled post-install
+- Stack apps install via signed `.pkg`, run sandboxed where supported
+- Setup script idempotent (verified by re-run with no changes)
+
+## Upstream we depend on
+
+- **Apple macOS** — base, unmodified
+- **macOS Privacy Guide / privacy.sexy** — reference for hardening configs
+- **Lockdown Mode** — Apple-provided, documented and enabled