refactor(backend): rename consolidated_launch -> infra_launch (0081 review)

Mechanical rename addressing review 6141 on #519: "consolidated launch" was
unclear about what it composes. Rename the per-backend module
`consolidated_launch.py` -> `infra_launch.py` and the error
`ConsolidatedLaunchError` -> `InfraLaunchError` across all three backends and
their callers/tests. Unify the three identical per-backend error classes into
one `InfraLaunchError` defined in `backend/base.py` (re-exported by each
`infra_launch`) so the base backend can raise and catch a single shared type —
groundwork for the base owning the gateway-attach flow.

Add a glossary entry defining **infra** = the per-host gateway + orchestrator
service pair every bottle attaches to.

No behavior change.

Refs #516, #519.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/unit/test_backend_secret_reprovision.py

@@ -11,9 +11,9 @@ from types import SimpleNamespace
 from unittest.mock import Mock, patch
 
 from bot_bottle.orchestrator.reprovision import reprovision_bottles
-from bot_bottle.backend.firecracker import consolidated_launch as fc
-from bot_bottle.backend.macos_container import consolidated_launch as mac
-from bot_bottle.backend.docker import consolidated_launch as docker
+from bot_bottle.backend.firecracker import infra_launch as fc
+from bot_bottle.backend.macos_container import infra_launch as mac
+from bot_bottle.backend.docker import infra_launch as docker
 from bot_bottle.orchestrator.client import OrchestratorClientError
 
 
@@ -132,7 +132,7 @@ class TestFirecrackerReprovision(unittest.TestCase):
     def test_persist_failure_is_fatal_to_launch(self) -> None:
         with patch.object(fc.util, "ssh_base_argv", return_value=["ssh", "guest"]), \
              patch.object(fc.subprocess, "run", return_value=_proc(1, stderr="denied")):
-            with self.assertRaisesRegex(fc.ConsolidatedLaunchError, "denied"):
+            with self.assertRaisesRegex(fc.InfraLaunchError, "denied"):
                 fc.persist_env_var_secret(Path("/key"), "10.0.0.1", "secret")
 
     def test_reads_live_vm_key_and_reprovisions(self) -> None: