feat(translate,scheduler,trace): new-key-only mode, stale PENDING protection, trace_id propagation

Translations:
- FR-045: new-key-only execution mode — translate only rows with unseen keys
- Compare source row keys against TranslationRecord.source_data from last succeeded run
- Baseline expired (>90 days) fallback to full mode with baseline_expired event
- run_noop early return when zero new keys (skip LLM + SQL)

Scheduler reliability:
- Stale PENDING protection: runs older than 1h auto-marked FAILED, no longer block schedule
- load_schedules() reloads active translation schedules from DB on restart
- add_translation_job/remove_translation_job register/unregister with APScheduler
- execution_mode column on translation_schedules with additive DB migration

Automation view:
- GET /settings/automation/translation-schedules endpoint
- Translation schedules displayed on Automation page below validation policies

Trace propagation:
- seed_trace_id() in all background entry points:
  TaskManager._run_task/_flusher_loop, SchedulerService._trigger_backup,
  websocket_endpoint, IdMappingService, all standalone scripts

Migrations:
- dictionary_entries: origin_run_id, origin_row_key, origin_user_id
- translation_schedules: execution_mode

Tests:
- 3 new test modules (22 tests): core_scheduler, executor_filter, scheduler_execution+guard
- Fix pre-existing translate test isolation (conftest.py)
- Fix test_list_runs_filter_status parameter

backend/src/scripts/clean_release_tui.py

@@ -19,6 +19,7 @@ BACKEND_ROOT = os.path.abspath(os.path.join(SCRIPT_DIR, "..", ".."))
 if BACKEND_ROOT not in sys.path:
     sys.path.insert(0, BACKEND_ROOT)
 
+from src.core.cot_logger import seed_trace_id
 from src.models.clean_release import (
     CandidateArtifact,
     CheckFinalStatus,
@@ -662,6 +663,7 @@ def tui_main(stdscr: curses.window):
 
 
 def main() -> int:
+    seed_trace_id()
     # TUI requires interactive terminal; headless mode must use CLI/API flow.
     if not sys.stdout.isatty():
         print(