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.py

@@ -0,0 +1,57 @@
+"""Phase state machine. Each phase is a (name, callable) pair; callables take
+the InstallContext and either return cleanly or raise to abort the install."""
+
+from __future__ import annotations
+
+import json
+import time
+import traceback
+from collections.abc import Callable
+from pathlib import Path
+
+from .context import InstallContext
+from .ui import error, info
+
+
+PhaseFn = Callable[[InstallContext], None]
+
+
+class PhaseError(Exception):
+    """Raised when a phase fails. Wrapped with the phase name."""
+
+
+def run(ctx: InstallContext, phases: list[tuple[str, PhaseFn]]) -> None:
+    ctx.state_dir.mkdir(parents=True, exist_ok=True)
+    state_path = ctx.state_dir / "state.json"
+    state = {"started_at": time.time(), "phases": []}
+    _write_state(state_path, state)
+
+    for name, fn in phases:
+        info(f"› {name}")
+        started = time.time()
+        try:
+            fn(ctx)
+        except Exception as exc:  # noqa: BLE001
+            elapsed = time.time() - started
+            state["phases"].append({
+                "name": name,
+                "status": "failed",
+                "elapsed": elapsed,
+                "error": str(exc),
+            })
+            _write_state(state_path, state)
+
+            error(f"Phase '{name}' failed after {elapsed:.1f}s: {exc}")
+            traceback.print_exc()
+            raise PhaseError(f"phase {name} failed: {exc}") from exc
+
+        elapsed = time.time() - started
+        state["phases"].append({"name": name, "status": "ok", "elapsed": elapsed})
+        _write_state(state_path, state)
+
+    state["finished_at"] = time.time()
+    _write_state(state_path, state)
+
+
+def _write_state(path: Path, state: dict) -> None:
+    path.write_text(json.dumps(state, indent=2, default=str))