Add opt-in outbound client mode for obs-websocket

[rowdytomato]

Description

Implements opt-in outbound websocket client mode while preserving existing protocol semantics:

• OBS sends Hello
• Controller sends Identify
• Request/event flow remains unchanged

Client mode is opt-in and default-off.

This PR adds:

• Shared protocol handling used by both server/client transports
• Outbound client transport with reconnect/backoff and heartbeat behavior
• Settings/config updates for outbound URL, auth, TLS, and explicit unsafe toggles
• TLS build toggle support for client mode
• Documentation and locale/string updates

Motivation and Context

Today, obs-websocket is primarily used with inbound connections to OBS.
Some deployments cannot expose inbound ports (NAT/firewall/restricted environments).
Outbound client mode enables those users to connect safely to a remote controller while keeping the existing protocol model and compatibility expectations.

How Has This Been Tested?

Validation covered inbound-server regression and outbound-client mode on Linux and Windows with TLS enabled and disabled.

• Inbound server-mode regression:
  • External client connects to OBS websocket server
  • Performs identify/auth flow
  • Executes core request path (GetVersion)
• Outbound client-mode:
  • OBS connects to external websocket endpoint
  • Completes Hello -> Identify -> Identified handshake
  • Verifies normal message flow and reconnect behavior
• TLS coverage:
  • TLS enabled and disabled builds/runs
  • Runtime behavior validated for secure and explicitly-unsafe toggles
• Manual settings checks:
  • Enable/disable client mode
  • URL/auth field validation
  • Status transitions and failure handling

Tested OS(s):

• Ubuntu 24.04.3 LTS (WSL2 + dockerized OBS build/runtime path)
• Windows 11 Version 25H2 (x64, native build/runtime validation)

Known Follow-up (Not in This PR)

Official release packaging for TLS-enabled client-mode artifacts may still require a companion obs-studio change (submodule bump and relevant preset/CI enablement).

Types of changes

• Code cleanup (non-breaking change which makes code smaller or more readable)
• Documentation change (a change to documentation pages)
• Other Enhancement (anything not applicable to what is listed)

Checklist:

• I have read the Contributing Guidelines.
• All commit messages are properly formatted and commits squashed where appropriate.
• My code is not on master or a release/* branch.
• The code has been tested.
• I have included updates to all appropriate documentation.