fix(gateway): respect streaming.enabled: false even when display.streaming is true (fixes #8338)

[iacker]

Summary

• The streaming gate in gateway/run.py now respects streaming.enabled: false even when display.streaming: true is set
• _scfg.enabled remains a hard prerequisite — per-platform display overrides can only disable streaming, not re-enable it when the global config has disabled it

Root cause

The ternary expression:

_streaming_enabled = (
    _scfg.enabled and _scfg.transport != "off"
    if _plat_streaming is None
    else bool(_plat_streaming)
)

When _plat_streaming was not None (display override existed), the global _scfg.enabled check was completely bypassed.

Fix

_global_streaming = _scfg.enabled and _scfg.transport != "off"
_streaming_enabled = (
    _global_streaming
    if _plat_streaming is None
    else _global_streaming and bool(_plat_streaming)
)

Testing

• New tests: tests/gateway/test_display_config.py::TestStreamingGateGlobalOverride (6 test cases)
• Full suite: pytest tests/gateway/test_display_config.py -q → 33 passed

Fixes #8338

[teknium1]

Closing in favor of #9799, which salvages #8347 (asheriif's implementation) onto current main. Your PR was also a valid fix — the difference is that your approach AND-gates per-platform streaming with global streaming, which would prevent per-platform overrides from enabling streaming when the global is off. asheriif's approach fixes the bug at the resolver level instead, preserving that flexibility. Thanks for the contribution!