fix: make installed wheel self-contained + harden install.sh prereqs

Addresses the review on PR #481.

Self-contained wheel (review point 1): the gateway/infra/orchestrator
images build from a context that must hold bot_bottle/, pyproject.toml,
and the root-level Dockerfiles. Modules previously located these by
walking __file__ to the repo root, so an installed wheel (package in
site-packages, no repo root) passed `doctor` but failed `start`.

- Add bot_bottle/resources.py: build_root() returns the repo root in a
  checkout (unchanged) or a staged copy from the wheel's bundled
  _resources/ otherwise; dockerfile()/nix_netpool_module()/
  netpool_script() derive from it.
- setup.py bundles the root Dockerfiles, nix module, netpool script, and
  pyproject.toml into bot_bottle/_resources/ at build; MANIFEST.in ships
  them in the sdist.
- Route every _REPO_ROOT/_REPO_DIR call site (docker/macos launch, macos
  infra, firecracker infra_vm/infra_artifact/setup, orchestrator
  lifecycle/gateway) through resources. Checkout behavior is unchanged.

install.sh prerequisites (review point 2): check for git when installing
a git+ spec, and — before the pip fallback — that pip is usable and the
interpreter isn't externally managed (PEP 668), pointing at pipx.

Tests: test_resources covers checkout + staged-wheel layouts;
test_wheel_install builds the wheel, installs it into an isolated venv,
and asserts `doctor` runs and build_root() yields a valid context.
Running `start` end-to-end still needs a Docker/KVM host (CI).

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

bot_bottle/backend/firecracker/infra_vm.py

@@ -42,6 +42,7 @@ from dataclasses import dataclass
 from pathlib import Path
 from typing import Generator
 
+from ... import resources
 from ...log import die, info
 from ..docker import util as docker_mod
 from . import firecracker_vm, infra_artifact, netpool, util
@@ -65,7 +66,6 @@ _GUEST_GATEWAY_JWT_PATH = "/var/lib/bot-bottle/gateway-jwt"
 _GATEWAY_IMAGE = "bot-bottle-gateway:latest"
 _ORCHESTRATOR_IMAGE = "bot-bottle-orchestrator:latest"
 _ORCHESTRATOR_FC_IMAGE = "bot-bottle-orchestrator-fc:latest"
-_REPO_ROOT = Path(__file__).resolve().parents[3]
 
 # Per-role rootfs source image + the extra free space `mke2fs` leaves for the
 # guest to grow into. The orchestrator keeps buildah's large build slack; the
@@ -130,12 +130,13 @@ def build_infra_images_with_docker() -> None:
     orchestrator + buildah). The gateway VM boots the gateway image directly.
     The launch host uses this only in `BOT_BOTTLE_INFRA_BUILD=local` mode;
     `publish_infra` uses it off-host to produce the published artifacts."""
+    root = str(resources.build_root())
     docker_mod.build_image(
-        _ORCHESTRATOR_IMAGE, str(_REPO_ROOT), dockerfile="Dockerfile.orchestrator")
+        _ORCHESTRATOR_IMAGE, root, dockerfile="Dockerfile.orchestrator")
     docker_mod.build_image(
-        _GATEWAY_IMAGE, str(_REPO_ROOT), dockerfile="Dockerfile.gateway")
+        _GATEWAY_IMAGE, root, dockerfile="Dockerfile.gateway")
     docker_mod.build_image(
-        _ORCHESTRATOR_FC_IMAGE, str(_REPO_ROOT), dockerfile="Dockerfile.orchestrator.fc")
+        _ORCHESTRATOR_FC_IMAGE, root, dockerfile="Dockerfile.orchestrator.fc")
 
 
 def build_rootfs_dir(role: str) -> Path: