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/macos_container/launch.py

@@ -36,7 +36,6 @@ import dataclasses
 import os
 import subprocess
 from contextlib import ExitStack, contextmanager
-from pathlib import Path
 from typing import Callable, Generator
 
 from ...bottle_state import (
@@ -49,6 +48,7 @@ from ...git_gate import GitGate
 from ...gateway.git_gate.http_backend import DEFAULT_PORT as _GIT_HTTP_PORT
 from ...image_cache import check_stale
 from ...log import die, info, warn
+from ... import resources
 from .. import BottleImages
 from ...supervisor.types import SUPERVISE_PORT
 from ..docker.egress import EGRESS_PORT
@@ -71,7 +71,6 @@ from .consolidated_launch import (
     deprovision_consolidated,
 )
 
-_REPO_DIR = str(Path(__file__).resolve().parent.parent.parent.parent)
 _AGENT_SLEEP_SECONDS = "2147483647"
 
 
@@ -94,7 +93,7 @@ def _agent_image(plan: MacosContainerBottlePlan) -> str:
             )
         info(f"using cached agent image {plan.image!r}")
         return plan.image
-    container_mod.build_image(plan.image, _REPO_DIR, dockerfile=plan.dockerfile_path)
+    container_mod.build_image(plan.image, str(resources.build_root()), dockerfile=plan.dockerfile_path)
     return plan.image