* fix(cli,core): restore default debug log file output
* fix(cli): preserve debug log sandbox opt-out
* test(cli): stabilize flaky UI tests
* fix(cli): scope default debug log to debug mode
* fix(core): scope debug log default to --debug mode per #6600
Revert isDebugLogFileEnabled() guard from `value === undefined` back to
`!value` so the non-debug default stays opt-in as prescribed in #6600.
The --debug scoping in config.ts already sets QWEN_DEBUG_LOG_FILE=1 when
in debug mode, making the global default flip unnecessary.
Also adds a regression test for the opt-out edge case
(QWEN_DEBUG_LOG_FILE='0' + --debug should not overwrite).
* test(cli): remove unused voice keyterms import
* test(cli): isolate cli entry fallback test
* ci: avoid web-shell smoke port collisions
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Co-authored-by: Shaojin Wen <shaojin.wensj@alibaba-inc.com>