refactor(gateway): fail closed without an orchestrator URL; drop stale single-tenant comments

Follow-ups from the #402 review of the single-tenant data-plane teardown.

- egress_entrypoint.sh: refuse to launch mitmdump when
  BOT_BOTTLE_ORCHESTRATOR_URL is unset, so the fail-closed guarantee no
  longer rests solely on mitmproxy's errorcheck addon exiting on the
  addon's load-time raise. A misconfigured gateway can never come up as
  a bare TLS-bumping open proxy with no policy.
- orchestrator/gateway.py: ensure_running() raises GatewayError on an
  empty orchestrator URL — a URL-less launch would only crash-loop the
  now-resolver-only daemons (egress raises, git-http exits 1, supervise
  exits 2). The env-injection branch is now unconditional.
- Drop stale "single-tenant" / "reads routes.yaml" comments in
  gateway.py and egress_entrypoint.sh, and the /etc/egress/routes.yaml
  layout line in Dockerfile.gateway.
- Tests: gateway fixtures supply an orchestrator URL; add a
  refuse-without-URL test and assert the URL env is injected.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UoEZHDjv84ChoZbozQERhJ

bot_bottle/egress_entrypoint.sh

@@ -15,11 +15,23 @@
 #     mitmproxy at it. The option REPLACES mitmproxy's default
 #     trust store, so passing the upstream CA alone would break
 #     non-chained hosts.
-#   * `-s /app/egress_addon.py` loads the addon that reads
-#     /etc/egress/routes.yaml.
+#   * `-s /app/egress_addon.py` loads the addon that resolves each
+#     request's policy from the orchestrator control plane by source
+#     IP (PRD 0070). There is no static routes file.
 
 set -e
 
+# Fail closed on a missing policy source. The addon itself raises at
+# load when BOT_BOTTLE_ORCHESTRATOR_URL is unset (so mitmdump exits via
+# its errorcheck addon), but that leaves the fail-closed guarantee at the
+# mercy of a mitmproxy version keeping that behavior. Refuse here too, so
+# a misconfigured gateway can never come up as a bare TLS-bumping open
+# proxy with no policy — independent of mitmproxy's startup-error handling.
+if [ -z "$BOT_BOTTLE_ORCHESTRATOR_URL" ]; then
+  echo "egress: BOT_BOTTLE_ORCHESTRATOR_URL is required (no static routes fallback)" >&2
+  exit 1
+fi
+
 # Pin mitmproxy's config dir to the bind-mount location of its CA
 # regardless of which user mitmdump runs as. In the legacy
 # four-daemon setup (Dockerfile.egress, USER mitmproxy) this