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/gateway.py

@@ -10,9 +10,10 @@ from ...paths import (
     ORCHESTRATOR_AUTH_JWT_ENV,
     host_gateway_ca_dir,
 )
+from ... import resources
 from ...gateway import (
   Gateway, GatewayTransport, GATEWAY_IMAGE, GATEWAY_NAME, GATEWAY_NETWORK,
-  GATEWAY_DOCKERFILE, REPO_ROOT, GATEWAY_LABEL, MITMPROXY_HOME,
+  GATEWAY_DOCKERFILE, GATEWAY_LABEL, MITMPROXY_HOME,
   DEFAULT_CA_TIMEOUT_SECONDS, CA_POLL_SECONDS, GATEWAY_CA_CERT, GatewayError
 )
 
@@ -50,7 +51,9 @@ class DockerGateway(Gateway):
         # `address` / `stop` work on an already-running gateway without it.
         self._orchestrator_url = ""
         self._gateway_token = ""
-        self._build_context = build_context or REPO_ROOT
+        # Resolved lazily in ensure_built() so merely constructing a gateway to
+        # read its CA never stages a build root from an installed wheel.
+        self._build_context = build_context
         self._dockerfile = dockerfile
         # Ports published on the host (0.0.0.0). Used by the Firecracker
         # backend's dev-harness gateway so VMs can reach it via their TAP link;
@@ -72,9 +75,10 @@ class DockerGateway(Gateway):
         forces a full rebuild (parity with `start --no-cache`)."""
         if self._dockerfile is None:
             return
+        context = self._build_context or resources.build_root()
         argv = ["docker", "build", "-t", self.image_ref,
-                "-f", str(self._build_context / self._dockerfile),
-                str(self._build_context)]
+                "-f", str(context / self._dockerfile),
+                str(context)]
         if os.environ.get("BOT_BOTTLE_NO_CACHE"):
             argv.insert(2, "--no-cache")
         proc = run_docker(argv)