docs(naming): adopt OS / Enhanced product-line framing + align with existing repos

Two product lines, named to make scope obvious to buyers:
- 🔒 SilverMetal OS — we ship the operating system or ROM
  (Linux, Pixel, Samsung-unlocked, Motorola-unlocked)
- 🛡️ SilverMetal Enhanced — we harden the OS the device already runs
  (Windows, macOS, iOS, generic Android)

Repo alignment:
- SilverVPN already exists as a SilverLABS product (server + MAUI client +
  Linux client + tunnel service). stack/vpn/ is now an integration pointer
  rather than a re-scaffold; per-platform READMEs reference it.
- SilverApple is deprecated; SilverMetal Enhanced — iOS supersedes it.
  Migration step added as roadmap milestone 3I.1.
- SilverDROID name clash explicitly noted as unrelated (it's the SilverSHELL
  AppStore Android client, not an Android ROM).
- SilverChat may overlap with SilverVPN.Client.Chat; alignment decision
  added as roadmap milestone 1.1.1.

Roadmap restructured: phases now track the OS/Enhanced split.
Platform matrix re-sectioned and decision flowchart updated.
README rewritten around the two-product-line framing.

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

macos/README.md

@@ -1,8 +1,10 @@
-# SilverMetal macOS
+# SilverMetal Enhanced — macOS
 
-**Status**: Phase 4 (planning, post-Windows v1)
+**Status**: Phase 3M (planning, post-Linux v1)
 
-Tier C-D — signed configuration profile + setup script + Stack ports. We cannot modify macOS; we configure everything Apple exposes.
+🛡️ **SilverMetal Enhanced product line** — we harden macOS in place. Apple's signed boot chain prevents an OS replacement.
+
+Tier C-D — signed configuration profile + setup script + Stack ports. We configure everything Apple exposes.
 
 ## Scope (v1)
 
@@ -14,6 +16,7 @@ Tier C-D — signed configuration profile + setup script + Stack ports. We canno
   - 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)
+- SilverVPN MAUI macOS client from existing [`SilverLABS/SilverVPN`](https://git.silverlabs.uk/SilverLABS/SilverVPN)
 - Setup guide for hardware-key 2FA, anti-forensics
 
 ## Out of scope
@@ -24,7 +27,7 @@ Tier C-D — signed configuration profile + setup script + Stack ports. We canno
 
 ## Directory layout
 
-To be populated in Phase 4:
+To be populated in Phase 3M:
 
 ```
 macos/
@@ -46,3 +49,4 @@ macos/
 - **Apple macOS** — base, unmodified
 - **macOS Privacy Guide / privacy.sexy** — reference for hardening configs
 - **Lockdown Mode** — Apple-provided, documented and enabled
+- **`SilverLABS/SilverVPN`** — MAUI macOS client (existing)