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_artifact.py

@@ -37,6 +37,7 @@ import urllib.error
 import urllib.request
 from pathlib import Path
 
+from ... import resources
 from ...log import die, info
 from . import util
 
@@ -44,8 +45,6 @@ from . import util
 # scheme can't collide with a cached/published artifact of the old one.
 _ARTIFACT_FORMAT = "1"
 
-_REPO_ROOT = Path(__file__).resolve().parents[3]
-
 # The two per-plane infra VM roles. Each publishes/pulls its own rootfs artifact
 # from its own generic package; the Dockerfiles baked into each differ (only the
 # orchestrator rootfs carries buildah), so the versions are hashed separately.
@@ -74,7 +73,7 @@ def local_build_requested() -> bool:
 
 
 def infra_artifact_version(
-    init_script: str, role: str, *, repo_root: Path = _REPO_ROOT,
+    init_script: str, role: str, *, repo_root: Path | None = None,
 ) -> str:
     """Content hash (16 hex) of everything baked into `role`'s infra rootfs: the
     whole shipped `bot_bottle` package, that role's Dockerfiles, and its guest
@@ -89,6 +88,8 @@ def infra_artifact_version(
     version or a launch host could boot a stale rootfs whose code differs from
     its checkout. `__pycache__`/`.pyc` are the only exclusions — build artifacts,
     never copied."""
+    if repo_root is None:
+        repo_root = resources.build_root()
     h = hashlib.sha256()
     h.update(f"format={_ARTIFACT_FORMAT}\nrole={role}\n".encode())
     pkg = repo_root / "bot_bottle"