[Feature] Syslog log sink — RFC 5424 over UDP, TCP and TLS

[pathosDev]

Part of the multi-sink logging effort (meta issue below). Builds on the core pipeline and
BatchingSink issues.

Why syslog

It is the one integration that needs no vendor at all: rsyslog, syslog-ng, journald's
forwarder, Papertrail and a long tail of network appliances all speak it. One sink covers
all of them.

Scope

src/logging/SyslogSink.ts + options family, extends BatchingSink.

RFC 5424 frame:

<134>1 2026-08-12T09:41:02.113Z host app-name 1234 - - order placed {orderId=42}

• PRI = facility * 8 + severity; severity mapped Debug → 7, Info → 6, Warn → 4,
  Error → 3; facility defaults to 16 (local0)
• RFC 3339 timestamp with millisecond precision
• HOSTNAME from options or the OS hostname; APP-NAME defaults to the system name;
  PROCID is the process id where available, else -; MSGID is -
• the structured-data element is deliberately - in v1: a well-formed SD-ID needs an IANA
  private enterprise number. Fields are appended to MSG as the same {k=v} suffix the
  text formatter uses. Documented, and revisitable if someone wants an enterprise id.

Transports:

• UDP via the same lazy node:dgram module type the GELF sink uses
• TCP / TLS via getTcpBackend().connect(...), with framing octet-counting
  (RFC 6587, <length> <frame>) or lf

Options: transport (udp | tcp | tls), host, port (514), facility, appName,
hostName, framing, tls (code-only), delivery. HOCON block
actor-ts.logger.sinks.syslog.

Acceptance criteria

• byte-exact frames for both framings, verified against the RFC's own example shape
• PRI arithmetic across facilities and all four levels
• a message containing a newline cannot break octet-counting framing
• UDP and TCP transports exercised through injectable seams, no network in tests
• docs section in observability/logging/integrations, EN + DE, noting the omitted
  structured-data element and why
• CHANGELOG entry
• bun run typecheck + bun test green on every commit; coverage gate before merge

Reference

• RFC 5424 (syslog protocol) — https://www.rfc-editor.org/rfc/rfc5424
• RFC 6587 (syslog over TCP framing) — https://www.rfc-editor.org/rfc/rfc6587

Part of #1150.