feat!: adopt Python 3.14 and 3.15 language features

- Require Python 3.15 for the server and Python 3.14 for the CLI.
- Match the server requirement to quart_common's Python 3.15 features.
- Replace future annotations with native deferred evaluation.
- Defer CLI command dependencies and QR imports on Python 3.15.
- Enable argparse suggestions for mistyped CLI commands.
- Remove the obsolete tomllib import fallback.
- Update my_helpers and quart_common submodule references.
- Lock test dependencies and exclude them from Docker installations.
- Add regression coverage for lazy imports and deferred annotations.
- Document runtime requirements and standalone CLI validation.
- Validate 276 tests on Python 3.15 and 18 CLI tests on Python 3.14.

BREAKING CHANGE: The server now requires Python 3.15+ and the standalone CLI requires Python 3.14+.

tests/test_python_features.py

@@ -0,0 +1,63 @@
+"""Exercise version-specific behavior in clean interpreters, not import stubs."""
+
+import os
+from pathlib import Path
+import subprocess
+import sys
+
+import pytest
+
+ROOT = Path(__file__).resolve().parents[1]
+
+def run_python(code):
+  env = os.environ.copy()
+  env['PYTHONPATH'] = os.pathsep.join([str(ROOT / 'cli'), str(ROOT)])
+  # Test the module opt-ins, independently of global import/color settings.
+  env.pop('PYTHON_LAZY_IMPORTS', None)
+  env['NO_COLOR'] = '1'
+  return subprocess.run(
+    [sys.executable, '-c', code], cwd=ROOT, env=env,
+    capture_output=True, text=True, check=True,
+  )
+
+def test_cli_typo_suggests_command():
+  result = run_python("""
+from nanoshare_client.cli import main
+try:
+  main(['uplod'])
+except SystemExit as exc:
+  assert exc.code == 2
+""")
+  assert "maybe you meant 'upload'" in result.stderr
+
+@pytest.mark.skipif(sys.version_info < (3, 15), reason='PEP 810 requires Python 3.15')
+def test_help_and_completion_do_not_load_network_or_watch_modules():
+  run_python("""
+import sys
+from nanoshare_client.cli import main
+try:
+  main(['--help'])
+except SystemExit as exc:
+  assert exc.code == 0
+assert main(['completion', 'bash']) == 0
+for name in ('httpx', 'nanoshare_client.auth', 'nanoshare_client.sync', 'nanoshare_client.watch'):
+  assert name not in sys.modules, name
+""")
+
+@pytest.mark.skipif(sys.version_info < (3, 15), reason='PEP 810 requires Python 3.15')
+def test_qr_import_is_lazy_but_rendering_still_works():
+  run_python("""
+import sys
+from link_composer.qr import make_qr_png
+assert 'qrcode' not in sys.modules
+assert make_qr_png('https://example.com').startswith(b'\\x89PNG')
+assert 'qrcode' in sys.modules
+""")
+
+def test_deferred_annotations_resolve_to_types():
+  run_python("""
+from typing import get_type_hints
+from my_modules.upload_content import MultipartUploadParts, parse_multipart_upload_body
+assert not isinstance(parse_multipart_upload_body.__annotations__['return'], str)
+assert get_type_hints(parse_multipart_upload_body)['return'] is MultipartUploadParts
+""")