refactor(orchestrator): rename Sidecar -> Gateway for the consolidated data plane

Retire "sidecar" for the consolidated per-host path (PRD 0070 naming
decision): the orchestrator is the umbrella/control plane, and the
egress/git/supervise data-plane unit it runs is the "gateway".

- git mv sidecar.py -> gateway.py and the two integration + one unit test
  files; DockerSidecar->DockerGateway, Sidecar->Gateway,
  SidecarError->GatewayError, SIDECAR_*->GATEWAY_*, ensure_sidecar->
  ensure_gateway, sidecar_status->gateway_status, container name
  bot-bottle-orch-sidecar->bot-bottle-orch-gateway.
- Prose rename across broker/registry/egress/policy_resolver + PRD 0070.
- Preserved: the image name bot-bottle-sidecars, the
  BOT_BOTTLE_SIDECAR_IMAGE env var, Dockerfile.sidecars, and PRD 0069's
  own stage-name cross-references (that doc still uses "sidecar").

No behavior change. Full unit suite green (1679 tests; the 13
test_sidecar_init /bin/sleep errors are pre-existing NixOS-local noise).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WBMWTEtQdJ4W5UrWuLHCck

bot_bottle/egress_addon_core.py

@@ -3,7 +3,7 @@
 Split out of `egress_addon.py` so the host's unit tests can
 exercise the parse + decision functions without depending on the
 `mitmproxy` package. The companion module wraps these with the
-`mitmproxy.http.HTTPFlow` API and is loaded inside the sidecar
+`mitmproxy.http.HTTPFlow` API and is loaded inside the gateway
 container.
 
 Imports: stdlib + `yaml_subset` (which is itself stdlib-only and
@@ -22,7 +22,7 @@ except ImportError:  # pragma: no cover - host-side path
     from .yaml_subset import YamlSubsetError, parse_yaml_subset
 
 # DLP detector-config parsing lives in a sibling module (also flat-bundled
-# into the sidecar — see Dockerfile.sidecars). Re-exported below so existing
+# into the gateway — see Dockerfile.sidecars). Re-exported below so existing
 # `from egress_addon_core import ON_MATCH_*` callers keep working.
 try:
     from egress_dlp_config import (  # type: ignore[import-not-found]
@@ -120,7 +120,7 @@ class ScanResult:
     reason: str
     location: str = ""  # where the match was found, e.g. "body", "authorization header"
     context: str = ""   # surrounding text with the match replaced by REDACT
-    # Raw substring the detector matched. Used inside the sidecar to key the
+    # Raw substring the detector matched. Used inside the gateway to key the
     # supervisor-approved "safe tokens" set (PRD 0062); never logged or written
     # to a proposal file. Empty for structural detectors (CRLF) that carry no
     # safelist-able value.
@@ -641,7 +641,7 @@ def outbound_scan_headers(
 ) -> dict[str, str]:
     """Return request headers that should be included in outbound DLP.
 
-    Routes that inject sidecar-owned auth always strip the agent's
+    Routes that inject gateway-owned auth always strip the agent's
     Authorization header before forwarding. Scanning that header first
     creates false positives for provider clients that insist on sending
     their own bearer-shaped placeholder, while still not changing what
@@ -692,7 +692,7 @@ def scan_outbound(
     crlf_text: str | None = None,
 ) -> ScanResult | None:
     # Lazy import to avoid circular deps and keep dlp_detectors optional
-    # at import time (the sidecar copies it flat alongside this file).
+    # at import time (the gateway copies it flat alongside this file).
     try:
         from dlp_detectors import (  # type: ignore[import-not-found]
             scan_crlf_injection,