refactor(de-sidecar): purge the "sidecar" name from live code, tests, and current docs

Completes the de-sidecar cleanup: no live code, test, current doc,
script, or nix file mentions or is named "sidecar" any more. Only the
dated PRD/research docs keep the term as historical record (agreed on
the #385 thread).

- Rename `sidecar_init.py`→`gateway_init.py` was done earlier; this pass
  sweeps the remaining descriptive uses: the egress / git-gate / supervise
  components are the gateway's *daemons*, the shared container is the
  *gateway*, the old per-bottle container was the *companion container*.
- Rename `tests/integration/test_sidecar_bundle_image.py`→`test_gateway_image.py`
  and its class; update `docs/ci.md` + `tests/README.md` for the renamed/
  removed integration tests.
- `SIDECAR_PORTS` shell var in `scripts/firecracker-netpool.sh`→`GATEWAY_PORTS`.

Full unit suite green (bar the pre-existing `/bin/sleep`-missing env
errors in test_gateway_init); docker integration — gateway singleton,
broker, real two-bottle multitenant isolation, and the gateway-image
build — all pass.

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

bot_bottle/backend/firecracker/bottle.py

@@ -7,7 +7,7 @@ session. `ssh -t` forwards the host terminal's SIGWINCH to the remote
 PTY natively, so no separate resize bridge is needed.
 
 Commands run as the image's `node` user via `runuser`, with HOME/USER/
-PATH and the bottle env (HTTPS_PROXY at the sidecar, CA paths, …) set
+PATH and the bottle env (HTTPS_PROXY at the gateway, CA paths, …) set
 per-invocation through `env` (the VM itself just runs the init; it has
 no baked-in process env like a `docker run` container would).
 """

bot_bottle/backend/firecracker/bottle_plan.py

@@ -13,7 +13,7 @@ from .. import BottlePlan
 class FirecrackerBottlePlan(BottlePlan):
     slug: str
     forwarded_env: dict[str, str] = field(repr=False)
-    # Stamped by launch once the sidecar is up and its ports are
+    # Stamped by launch once the gateway is up and its ports are
     # published on the host-side TAP IP (empty at prepare time).
     agent_proxy_url: str = ""
     agent_git_gate_url: str = ""
@@ -21,7 +21,7 @@ class FirecrackerBottlePlan(BottlePlan):
 
     @property
     def container_name(self) -> str:
-        """Instance name, reused for the sidecar container + VM run dir.
+        """Instance name, reused for the gateway container + VM run dir.
         Matches the `bot-bottle-<slug>` convention the other backends
         use so cleanup/enumerate discovery-by-prefix keeps working."""
         return self.agent_provision.instance_name

bot_bottle/backend/firecracker/enumerate.py

@@ -1,6 +1,6 @@
 """Active-agent enumeration for the Firecracker backend.
 
-The backend is disabled during the de-sidecar cleanup (#385) — it can't
+The backend is disabled during the companion-container removal (#385) — it can't
 launch bottles, so there are none to enumerate. Real enumeration returns
 with the backend's consolidated relaunch (#354).
 """

bot_bottle/backend/firecracker/launch.py

@@ -2,7 +2,7 @@
 
 The firecracker backend launched a per-bottle companion container (the
 egress / git-gate / supervise data plane) alongside each microVM. That
-per-bottle-companion architecture was removed in the de-sidecar cleanup;
+per-bottle-companion architecture was removed in the companion-container removal;
 firecracker's replacement — the consolidated per-host gateway — lands in
 its own cutover (#354).
 

bot_bottle/backend/firecracker/netpool.py

@@ -18,7 +18,7 @@ Topology (per slot i):
   * a /31 host<->guest link: host = base + 2i (the gateway the VM
     routes through), guest = base + 2i + 1 (the VM's address).
   * isolation via ``table inet bot_bottle_fc``: a VM reaches only its
-    own sidecar (DNAT'd from the host TAP IP) and nothing else.
+    own gateway (DNAT'd from the host TAP IP) and nothing else.
 
 The default IP block is ``10.243.0.0/16`` — an intentionally obscure
 corner of RFC-1918 private space. RFC-1918 is the range *designated*
@@ -88,7 +88,7 @@ def ip_base() -> str:
     return _cfg("BOT_BOTTLE_FC_IP_BASE")
 
 
-# Sidecar ports the VM reaches at its host-side TAP IP. Kept in sync
+# Gateway ports the VM reaches at its host-side TAP IP. Kept in sync
 # with the backend constants (egress 9099, supervise 9100, git-http
 # 9420); rendered into the setup output for operator visibility.
 GATEWAY_PORTS = (9099, 9100, 9420)