refactor(egress): make Egress a service class in an egress package

Split the flat egress.py into an egress/ package: neutral DTOs
(EgressRoute, EgressPlan) in plan.py, and the concrete Egress service
class plus rendering/env helpers in service.py, behind a thin
__getattr__ facade so leaf imports stay cheap.

Egress drops ABC and becomes a concrete service the backends call:
resolve_token_values / agent_env_entries / prepare are now methods.
Backend launch paths (docker, firecracker, macos_container) call
Egress().<method>(...) instead of the module-level functions.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

bot_bottle/egress/plan.py

@@ -0,0 +1,48 @@
+"""Egress launch DTOs (PRD 0017).
+
+`EgressRoute` (the host-side extension of the addon's wire `Route`) and
+`EgressPlan` (the launch plan the backend contract references). Pure value
+types — the route-building / rendering logic and the `Egress` service live in
+`egress.service`.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from pathlib import Path
+
+from ..gateway.egress_addon_core import Route
+
+
+@dataclass(frozen=True)
+class EgressRoute(Route):
+    """Host-side extension of the addon's `Route`.
+
+    Inherits `host`, `matches`, `auth_scheme`, and `token_env`
+    from `egress_addon_core.Route` — those are the fields that cross the
+    YAML wire into the gateway. The fields below are host-only and
+    are never serialised to the addon.
+
+    `token_ref` is the host env var the CLI reads at launch and forwards
+    into the container's environ under `token_env`.
+
+    `roles` carries the manifest route's role tuple (reserved for
+    future use; always empty today)."""
+
+    token_ref: str = ""
+    roles: tuple[str, ...] = ()
+
+
+@dataclass(frozen=True)
+class EgressPlan:
+    slug: str
+    routes_path: Path
+    routes: tuple[EgressRoute, ...]
+    token_env_map: dict[str, str]
+    internal_network: str = ""
+    egress_network: str = ""
+    mitmproxy_ca_host_path: Path = Path()
+    mitmproxy_ca_cert_only_host_path: Path = Path()
+    log: int = 0
+    canary: str = ""
+    canary_env: str = ""