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/docker/launch.py

@@ -33,7 +33,6 @@ from __future__ import annotations
 import dataclasses
 import os
 from contextlib import ExitStack, contextmanager
-from pathlib import Path
 from typing import Callable, Generator
 
 from ...agent_provider import runtime_for
@@ -65,10 +64,7 @@ from ...orchestrator.store.config_store import resolve_teardown_timeout
 from .consolidated_launch import launch_consolidated, deprovision_consolidated
 from .infra import INFRA_NAME
 from .gateway import DockerGateway
-
-
-# Where the repo root lives, for `docker build` context. Computed once.
-_REPO_DIR = str(Path(__file__).resolve().parent.parent.parent.parent)
+from ... import resources
 
 
 def build_or_load_images(plan: DockerBottlePlan) -> BottleImages:
@@ -88,7 +84,7 @@ def build_or_load_images(plan: DockerBottlePlan) -> BottleImages:
             )
         info(f"using cached agent image {plan.image!r}")
         return BottleImages(agent=plan.image)
-    docker_mod.build_image(plan.image, _REPO_DIR, dockerfile=plan.dockerfile_path)
+    docker_mod.build_image(plan.image, str(resources.build_root()), dockerfile=plan.dockerfile_path)
     docker_mod.verify_agent_image(
         plan.image, runtime_for(plan.agent_provider_template).smoke_test,
     )