Scaffold Python orchestrator + split install.sh / finalize.sh

Chunk 1 of the C3 refactor: replace the two-pass install model (archinstall
CLI + custom shell dance + chroot bash installer) with a single Python
orchestrator that owns phase ordering, using archinstall as a library
subsystem.

Splits the bash entry point into two:
- install.sh: online entry point. Ensures omarchy runtime + base.packages
  are installed/up to date, then exec's finalize.sh.
- finalize.sh: the in-target portion (preflight + packaging + config +
  login + post-install). Called by install.sh (online) AND by the
  orchestrator after arch-chroot -u $USER (offline).

Adds the orchestrator skeleton under install/orchestrator/:
- main.py: entry point, builds + runs the phase list
- context.py: InstallContext (parsed configurator JSON + invocation paths)
- phases.py: phase state machine (logging + state.json + error wrapping)
- phases_impl.py: stubbed phase implementations (filled in by chunks 2-6)
- archinstall_adapter.py: thin compat wall around archinstall lib imports
  (only this module imports from archinstall.*)
- ui.py: gum subprocess wrappers so the orchestrator keeps the same
  styled-terminal UX as the bash installer

Updates bin/omarchy-install to dispatch:
- --config <json> in args → python -m orchestrator.main (ISO install)
- anything else → bash install.sh (online rerun on installed system)

Concrete phase logic lands in subsequent chunks. All phases currently
raise NotImplementedError; the orchestrator imports cleanly and --help
works as a smoke check.

install/orchestrator/archinstall_adapter.py

@@ -0,0 +1,37 @@
+"""Thin compatibility wall around the archinstall Python library.
+
+ONLY this module imports from archinstall. Everything else uses these functions.
+If archinstall's API churns, the blast radius is contained here.
+
+Tested against archinstall 4.3 (Python 3.14).
+"""
+
+from __future__ import annotations
+
+# Phase 2 will populate this module. For now we declare the contract so the
+# rest of the orchestrator can be wired up against the eventual surface area.
+
+
+def prepare_live() -> None:
+    """pacman-key init/populate, mount checks, etc. Currently a no-op stub."""
+    raise NotImplementedError("populated in Chunk 2")
+
+
+def cleanup_disk() -> None:
+    raise NotImplementedError("populated in Chunk 2")
+
+
+def create_partitions_and_mounts(install_ctx) -> None:
+    raise NotImplementedError("populated in Chunk 2")
+
+
+def install_base_system(install_ctx) -> None:
+    raise NotImplementedError("populated in Chunk 2")
+
+
+def install_limine_bootloader(install_ctx) -> None:
+    raise NotImplementedError("populated in Chunk 2")
+
+
+def create_users(install_ctx) -> None:
+    raise NotImplementedError("populated in Chunk 2")