Review architecture specs, address critical/warning issues, mark reviewed

Address 5 critical and 7 warning issues from architecture review:
- Fix duplicate sentence in napi-and-pubsub.md server side section
- Add wraith- namespace reservation to server.md constraints (ADR-018)
- Document stealth mode TLS-only requirement in server.md
- Create ADR-019 for --proxy dual semantics (client vs server)
- Clarify NAPI connect() vs CLI wraith connect distinction
- Add SOCKS5h default as privacy design decision in client.md
- Expand reconnection section (always-on, re-register port forwards)
- Add graceful shutdown sections to client.md and server.md
- Specify OpenSSH key format for path-or-buffer inputs across all docs
- Resolve pubsub alternative approach ambiguity (ADR-018 is primary)
- Replace server.md handler impl block with behavioral description
- Standardize iroh endpoint ID terminology (base58-encoded)
- Remove iroh API implementation details from transport.md/server.md
- Add error handling pattern as cross-cutting concern in overview.md
- Update all document statuses from draft to reviewed

docs/architecture/open-questions.md

@@ -1,6 +1,6 @@
 ---
-status: draft
-last_updated: 2026-06-01
+status: reviewed
+last_updated: 2026-06-02
 ---
 
 # Open Questions