feat(orchestrator): authoritative failure-count badge endpoint (DEBT-042)

New GET /api/v1/orchestrator/events/stats?since=1h&success=false&kind=...
backed by repo.count_orchestrator_failures(since_ts, kind), which
counts failed rows across both orchestrator_events and
orchestrator_emails since the cutoff.

Window parser accepts ^\d+[smhd]$, capped at 7d. Today only
success=false is accepted on this surface so the endpoint isn't
accidentally repurposed before the next consumer is properly
designed.

Orchestrator.tsx polls the endpoint on mount + every 30 s and
renders the authoritative DB-derived count instead of deriving from
the in-memory SSE buffer + one paginated page (which silently
excluded failures older than the local window).

decnet/web/router/__init__.py

@@ -32,6 +32,7 @@ from .campaigns.api_list_campaign_identities import router as campaign_identitie
 from .campaigns.api_events import router as campaign_events_router
 from .orchestrator.api_list_events import router as orchestrator_list_router
 from .orchestrator.api_events import router as orchestrator_events_router
+from .orchestrator.api_event_stats import router as orchestrator_stats_router
 from .realism.api_config import router as realism_config_router
 from .realism.api_personas import router as realism_personas_router
 from .realism.api_synthetic_files import router as realism_synthetic_files_router
@@ -123,6 +124,7 @@ api_router.include_router(campaign_identities_router)
 api_router.include_router(campaign_events_router)
 api_router.include_router(orchestrator_list_router)
 api_router.include_router(orchestrator_events_router)
+api_router.include_router(orchestrator_stats_router)
 
 # Realism — global persona pool CRUD for the dashboard's
 # "Persona Generation" page.  The orchestrator reads from the same