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>

linux/README.md

@@ -1,7 +1,9 @@
-# SilverMetal Linux
+# SilverMetal OS — Linux
 
 **Status**: Phase 1 (planning) → moving to milestone 1.1 (reproducible Kicksecure fork build)
 
+🔒 **SilverMetal OS product line** — we ship the operating system.
+
 The reference SilverMetal flavour. Tier A — full kernel-level hardening, verified boot we control, Debian/Kicksecure-based.
 
 ## Scope (v1)
@@ -19,6 +21,8 @@ See [`../docs/roadmap.md`](../docs/roadmap.md) Phase 1.
 - nftables default-deny inbound, encrypted DNS, SilverVPN always-on default
 - Zero upstream telemetry — verified by integration test
 - SilverBrowser default (ungoogled-chromium-rebranded v1)
+- SilverVPN integrated from existing [`SilverLABS/SilverVPN`](https://git.silverlabs.uk/SilverLABS/SilverVPN) (Linux client + tunnel service)
+- SilverSync v1 (Nextcloud-backed, client-side encryption)
 - A/B updates with rollback, signed by our keys
 - Optional amnesic session mode
 
@@ -65,3 +69,4 @@ linux/
 - **GrapheneOS hardened_malloc** — allocator
 - **KSPP** — kernel config authority
 - **secureblue** — reference for v1.1 immutable design
+- **`SilverLABS/SilverVPN`** — VPN client + tunnel service (existing, integrated)