pivot to Python: replace Kotlin/JVM with stdlib zipapp

Reasons stacked up:
  - AV: unsigned JARs that auto-download binaries + upload files trigger
    Windows Defender false-positives more often than Python scripts
    invoked by code-signed python.exe.
  - Qt UI option: PySide6 opens a path to a real Qt UI (matching Prism's
    look) if needed later. JVM Qt bindings are abandoned.
  - frazclient already needs Python; inlining as 'import cloud_sync' is
    zero overhead vs the launcher always shelling out to java.

Implementation:
  - cloud_sync package: cli.py (argparse), creds.py, scope.py,
    restic.py (binary discovery + auto-download + sha256 verify),
    sync.py (pull/push subprocess restic).
  - pyproject.toml with hatchling backend; pip-installable.
  - Makefile builds cloud-sync.pyz via python -m zipapp (~53 KB).
  - 33 pytest tests, stdlib only on runtime.
  - CI workflow runs pytest matrix (3.10/3.11/3.12) + builds pyz.
  - DESIGN.md + README.md updated to reflect Python.

E2E verified against local restic-rest-server:
  pull empty → push initial → rm -rf local → pull restores → modify+push
  creates second snapshot → client forget --prune blocked by --append-only.

Throws away ~565 LOC of Kotlin (and 18 jar tests) committed earlier in
this same session. Net result is ~250 LOC Python + 33 tests = smaller
and more aligned with the rest of the stack.

tests/test_scope.py

@@ -0,0 +1,70 @@
+"""Scope file reader + materializer tests."""
+
+from __future__ import annotations
+
+import json
+
+from cloud_sync.scope import (
+    DEFAULT_EXCLUDE,
+    DEFAULT_INCLUDE,
+    Scope,
+    load,
+    materialize_for_restic,
+)
+
+
+def test_load_missing_returns_defaults(tmp_path):
+    s = load(tmp_path)
+    assert s.include == DEFAULT_INCLUDE
+    assert s.exclude == DEFAULT_EXCLUDE
+
+
+def test_load_valid_overrides_defaults(tmp_path):
+    state = tmp_path / ".cloud-sync"
+    state.mkdir()
+    (state / "scope.json").write_text(json.dumps({
+        "include": ["foo/", "bar.txt"],
+        "exclude": ["**/*.log"],
+    }))
+    s = load(tmp_path)
+    assert s.include == ["foo/", "bar.txt"]
+    assert s.exclude == ["**/*.log"]
+
+
+def test_load_partial_keeps_defaults_for_missing(tmp_path):
+    state = tmp_path / ".cloud-sync"
+    state.mkdir()
+    (state / "scope.json").write_text(json.dumps({"include": ["just-this"]}))
+    s = load(tmp_path)
+    assert s.include == ["just-this"]
+    assert s.exclude == DEFAULT_EXCLUDE
+
+
+def test_load_invalid_falls_back(tmp_path, capsys):
+    state = tmp_path / ".cloud-sync"
+    state.mkdir()
+    (state / "scope.json").write_text("{not valid json")
+    s = load(tmp_path)
+    assert s.include == DEFAULT_INCLUDE
+    captured = capsys.readouterr()
+    assert "invalid" in captured.err.lower()
+
+
+def test_materialize_writes_files(tmp_path):
+    scope = Scope(include=["config/", "options.txt"], exclude=["**/*.log"])
+    files_from, exclude_from = materialize_for_restic(tmp_path, scope)
+    assert files_from.exists()
+    assert exclude_from.exists()
+    body_in = files_from.read_text().splitlines()
+    body_ex = exclude_from.read_text().splitlines()
+    # trailing slash stripped on include entries
+    assert "config" in body_in
+    assert "options.txt" in body_in
+    assert "**/*.log" in body_ex
+
+
+def test_materialize_creates_state_dir(tmp_path):
+    scope = Scope(include=["x"], exclude=["y"])
+    files_from, _ = materialize_for_restic(tmp_path, scope)
+    assert files_from.parent.name == ".cloud-sync"
+    assert files_from.parent.exists()