falco: add cryptominer/runtime-security scanner wired into netdata

Detects unauthorized miners (and other runtime threats) via Falco's
syscall/eBPF monitoring, following the 2026-08-06 gitea/xmrig
compromise. Wired into netdata rather than a new notification channel:
Falco exposes a Prometheus /metrics endpoint, netdata scrapes it, and a
new health.d alarm pages through netdata's already-configured Telegram
bot - no new alerting infra needed.

Includes a custom process-name rule for known miner binaries (the stock
Stratum-protocol rule wouldn't have caught the actual gitea incident,
which used a bare host:port with no scheme prefix), an outbound
miner-pool-port rule as a second layer, and rule_matching: all in the
Falco config - without it, Falco silently drops all but the first
matching rule per event, which would have suppressed our custom rule
whenever a stock rule also matched the same process.

falco/rules/tune-noise.yaml

@@ -0,0 +1,13 @@
+# Tune out stock-rule false positives observed on this specific host, so the
+# broad netdata "any Falco match" alarm only pages for things worth paging
+# for. Uses Falco's own user_* customization macros rather than disabling
+# whole rules, so the underlying security check stays active for everything
+# else. Add entries here as new noisy defaults turn up - don't let this list
+# grow into blinding Falco to anything actually meaningful.
+
+# "Sensitive file opened for reading by non-trusted program" fired every
+# ~10s from inbox-zero-db's pg_isready healthcheck touching /etc/shadow -
+# NSS/libc user-lookup behavior during process init, not credential
+# harvesting. Scoped to just this binary, not a blanket rule disable.
+- macro: user_known_read_sensitive_files_activities
+  condition: (proc.name = pg_isready)