docs(chat): adopt existing SilverVPN.Client.Chat as SilverChat — promote to v1

Inspection of ../SilverVPN/clients/SilverVPN.Client.Chat reveals a mature,
production-grade SilverChat implementation:

- Cross-platform MAUI client (Windows / macOS / Android / iOS)
- 13 ViewModels + 13 Views — feature-complete UX (contacts, conversations,
  group chat, invites, safety numbers, settings, login)
- Signal Protocol crypto: Double Ratchet, X3DH (PreKey + Identity stores),
  Safety Numbers, encrypted attachments
- VpnChatTransport — chat carried over the SilverVPN tunnel itself,
  eliminating third-party metadata exposure
- Server-side already in SilverVPN.Api: ChatHub (SignalR), ChatController,
  ChatAttachmentController, ContactsController
- Windows MSI installer wired (installer/silverchat/SilverChat.wxs)

Decision: adopt-as-is, do not duplicate. SilverChat is more advanced than
the v1.1 plan (which considered Matrix / Signal-fork) — three wins:
1. Signal Protocol natively, not a tentative fork
2. Chat over the VPN tunnel — better metadata hygiene
3. Cross-platform on day one

Changes:
- stack/chat/README.md rewritten as integration pointer (mirror of stack/vpn/)
- stack/README.md status table updated; SilverChat promoted v1.1 → v1
- docs/roadmap.md: new milestone 1.9 (Chat integration into Linux v1);
  Phase 1.1 alignment-review milestone removed (resolved by this finding);
  remaining 1.1 milestones renumbered
- root README.md: Stack table + Status table updated

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

docs/roadmap.md

@@ -33,10 +33,11 @@ The two product lines (**SilverMetal OS** and **SilverMetal Enhanced**) share th
 | 1.6 | SilverBrowser v1 integrated (ungoogled-chromium rebrand) | Default browser, no Google services, fingerprint defences validated |
 | 1.7 | SilverVPN integrated into image | Existing `SilverLABS/SilverVPN` Linux client + tunnel service preinstalled, always-on default; kill-switch verified |
 | 1.8 | SilverSync v1 integrated (Nextcloud backbone, client-side encryption) | Contacts/calendar/files sync end-to-end; server cannot read content |
-| 1.9 | Update server + signing ceremony complete | First signed update delivered through alpha channel; rollback verified |
-| 1.10 | Public alpha ISO + SBOM + build attestation published | Download page live; reproducible-build instructions documented |
-| 1.11 | External privacy-engineering review | One independent reviewer (Kicksecure / Whonix community) signs off on threat-model fidelity |
-| 1.12 | Hardware SKU pilot batch | 10 preflashed Coreboot-supported laptops shipped and validated |
+| 1.9 | SilverChat integrated into image | Existing `SilverVPN.Client.Chat` packaged for Linux and integrated; SignalR hub reachable; first message sent and received over VPN tunnel transport |
+| 1.10 | Update server + signing ceremony complete | First signed update delivered through alpha channel; rollback verified |
+| 1.11 | Public alpha ISO + SBOM + build attestation published | Download page live; reproducible-build instructions documented |
+| 1.12 | External privacy-engineering review | One independent reviewer (Kicksecure / Whonix community) signs off on threat-model fidelity |
+| 1.13 | Hardware SKU pilot batch | 10 preflashed Coreboot-supported laptops shipped and validated |
 
 **Exit criteria for Phase 1**: alpha is publicly downloadable, all verification gates green, hardware SKU available for purchase.
 
@@ -46,13 +47,13 @@ The two product lines (**SilverMetal OS** and **SilverMetal Enhanced**) share th
 
 **Goal**: complete the SilverLABS Application Stack so v1.1 ships with the full suite.
 
+> **Note**: SilverChat was originally a Phase 1.1 milestone but has been **promoted to Phase 1** (milestone 1.9) — the existing `SilverVPN.Client.Chat` implementation is production-grade (Signal Protocol over VPN transport) and ready to integrate now.
+
 | # | Milestone | Done when |
 |---|---|---|
-| 1.1.1 | SilverChat v1 — alignment review | Decide whether to pull `SilverVPN.Client.Chat` in, fork it, or scope SilverChat as a separate effort. Outcome documented in `docs/decisions/` |
-| 1.1.2 | SilverChat v1 client + homeserver | Cross-platform clients functional; account-number onboarding |
-| 1.1.3 | SilverDuress v1 | Linux PAM module + Android duress PIN + iOS Shortcuts/MDM trigger + Windows Group Policy + macOS profile — all verified |
-| 1.1.4 | SilverKeys v1 | Bitwarden-derived client + SilverSync backend; per-platform clients |
-| 1.1.5 | Atomic root experiment | ostree-based variant builds; v1.2 candidate if successful |
+| 1.1.1 | SilverDuress v1 | Linux PAM module + Android duress PIN + iOS Shortcuts/MDM trigger + Windows Group Policy + macOS profile — all verified |
+| 1.1.2 | SilverKeys v1 | Bitwarden-derived client + SilverSync backend; per-platform clients |
+| 1.1.3 | Atomic root experiment | ostree-based variant builds; v1.2 candidate if successful |
 
 ---