feat(api): GET /credentials endpoint

Surfaces the Credential table (deduped attacker auth attempts) via
a new /api/v1/credentials route. Mirrors the Bounty cache pattern
(5s TTL on the unfiltered default page) and reuses the existing
get_credentials / get_total_credentials repo methods + the already
defined CredentialsResponse DTO. Filters: search, service, attacker_ip.

decnet/web/router/__init__.py

@@ -5,6 +5,7 @@ from .auth.api_change_pass import router as change_pass_router
 from .logs.api_get_logs import router as logs_router
 from .logs.api_get_histogram import router as histogram_router
 from .bounty.api_get_bounties import router as bounty_router
+from .credentials.api_get_credentials import router as credentials_router
 from .stats.api_get_stats import router as stats_router
 from .fleet.api_get_deckies import router as get_deckies_router
 from .fleet.api_mutate_decky import router as mutate_decky_router
@@ -59,6 +60,9 @@ api_router.include_router(histogram_router)
 # Bounty Vault
 api_router.include_router(bounty_router)
 
+# Credentials (deduped attacker auth attempts)
+api_router.include_router(credentials_router)
+
 # Fleet Management
 api_router.include_router(get_deckies_router)
 api_router.include_router(mutate_decky_router)