fix: no self-hosted ANIS model, license key is dashboard-only, remove dead ANIS_SHARE_ATTACKERS

Three corrections, driven by explicit product decisions plus code
verification:

- There is no self-hosted-ANIS deployment model going forward. ANIS_URL
  is now hardcoded to https://anis.weboria.eu in docker-compose.yml, not
  a customer-configurable env var -- removed from env.example and the
  README entirely.
- The ANIS license key is dashboard-only (Threat Intel -> ANIS
  Connection, write-only there per the earlier security fix) -- never
  set via .env. ANIS_LICENSE_KEY hardcoded to an empty string in
  docker-compose.yml (community tier by default) rather than left as a
  pass-through env var with no real path to ever being set.
- Removed ANIS_SHARE_ATTACKERS -- confirmed dead via grep, zero
  references anywhere in the Go source. This was incorrectly kept as
  "real" in the previous env.example cleanup pass; ROADMAP.md in the
  appliance repo already documented this exact variable as dead.

ANIS_ENABLED remains the one real customer-facing ANIS toggle.

env.example

@@ -26,15 +26,11 @@ TZ=UTC
 # Threat Intelligence (ANIS)
 # ===========================================
 # ARGUS connects to ANIS, Weboria's threat-intelligence network, by default
-# — no license key needed for the free Community tier. These three values
-# only matter on first boot; manage the connection afterward from
-# Threat Intel -> ANIS Connection in the dashboard.
+# — no license key needed for the free Community tier. There is no
+# self-hosted-ANIS deployment model, so there's no URL to configure here.
+# A license key upgrades the tier, but is only ever set from
+# Threat Intel -> ANIS Connection in the dashboard — never from this file.
 ANIS_ENABLED=true
-ANIS_URL=https://anis.weboria.eu
-ANIS_LICENSE_KEY=
-
-# Share this instance's confirmed attacker IPs back to the community feed?
-ANIS_SHARE_ATTACKERS=false
 
 # ===========================================
 # Network Ports