Host sandboxed CEF subprocesses in obs64

[summeroff]

Summary

• classify and dispatch CEF child invocations before normal OSN startup
• export the versioned sandbox lifecycle ABI from obs64.exe and link the host to OBS::cef-sandbox
• load only the packaged obs-browser.dll for child dispatch and reject malformed, unknown, duplicate, or --no-sandbox invocations
• isolate the /MD Crashpad implementation in osn-crashpad-bridge.dll so the /MT CEF sandbox can link safely
• add focused subprocess classification and install-path tests
• consume published libobs 32.1.1sl10cef1
• keep Chromium runtime dependencies out of the test that opens every actual OBS plugin module

Dependencies / draft status

• depends on Package and export Windows CEF sandbox support obs-studio#773
• pinned test artifact: libobs-windows64-release-32.1.1sl10cef1.7z
• artifact SHA-256: B347C8948B820E2C822366B4DABA1BD93FDF75F47E1C6B5F0FD9E4C4995AC23D
• remains draft pending Desktop runtime validation

Validation

• focused dispatcher suite: 24 assertions in 6 test cases
• against the published libobs package: complete Debug and Release builds
• full expanded native suite: 121/121 Release and 121/121 serialized Debug
• dependency baselines, ABI exports/imports, packaged runtime loading, and fail-closed exit codes checked locally
• GitHub Windows build passes against the published package
• GitHub Windows integration passes all 259 tests, including the corrected module-enumeration and CEF/browser cases

[summeroff]

Superseded by draft PR #1781 after renaming the source branch to remove the internal issue identifier. The commits and review fixes are preserved there.