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/setup.py

@@ -20,6 +20,7 @@ import subprocess
 import sys
 from pathlib import Path
 
+from ... import resources
 from . import netpool
 from . import util
 
@@ -42,13 +43,13 @@ def _has_systemd() -> bool:
 
 
 def _module_path() -> str:
-    """Absolute path to the importable NixOS module in this checkout."""
-    return str(Path(__file__).resolve().parents[3] / "nix" / "firecracker-netpool.nix")
+    """Absolute path to the importable NixOS module (checkout or wheel)."""
+    return str(resources.nix_netpool_module())
 
 
 def _script_path() -> str:
-    """Absolute path to the bundled bring-up script in this checkout."""
-    return str(Path(__file__).resolve().parents[3] / "scripts" / "firecracker-netpool.sh")
+    """Absolute path to the bundled bring-up script (checkout or wheel)."""
+    return str(resources.netpool_script())
 
 
 def _print_prereqs() -> None: