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/phases_impl.py

@@ -0,0 +1,63 @@
+"""Concrete phase implementations.
+
+Each function takes the InstallContext and either returns or raises. Phases are
+small wrappers — heavy lifting lives in archinstall_adapter (for Arch substrate
+work) and helpers.* (for Omarchy-specific work).
+
+Most are stubbed until Chunks 2–6 land. Keeping them here so the phase wiring
+in main.py is testable end-to-end as a smoke check ('every phase imports
+cleanly') from Chunk 1 onwards.
+"""
+
+from __future__ import annotations
+
+from . import archinstall_adapter as arch
+from .context import InstallContext
+
+
+def prepare_live(ctx: InstallContext) -> None:
+    raise NotImplementedError("Chunk 2")
+
+
+def cleanup_disk(ctx: InstallContext) -> None:
+    raise NotImplementedError("Chunk 2")
+
+
+def partition_and_mount(ctx: InstallContext) -> None:
+    raise NotImplementedError("Chunk 2")
+
+
+def install_base(ctx: InstallContext) -> None:
+    raise NotImplementedError("Chunk 2")
+
+
+def install_bootloader(ctx: InstallContext) -> None:
+    raise NotImplementedError("Chunk 2")
+
+
+def write_limine_config(ctx: InstallContext) -> None:
+    raise NotImplementedError("Chunk 3")
+
+
+def install_early_omarchy_packages(ctx: InstallContext) -> None:
+    raise NotImplementedError("Chunk 4")
+
+
+def create_user(ctx: InstallContext) -> None:
+    raise NotImplementedError("Chunk 2")
+
+
+def install_omarchy_runtime(ctx: InstallContext) -> None:
+    raise NotImplementedError("Chunk 4")
+
+
+def run_chroot_finalizer(ctx: InstallContext) -> None:
+    raise NotImplementedError("Chunk 5")
+
+
+def validate_boot(ctx: InstallContext) -> None:
+    raise NotImplementedError("Chunk 6")
+
+
+def finish(ctx: InstallContext) -> None:
+    raise NotImplementedError("Chunk 6")