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+.

README.md

@@ -0,0 +1,38 @@
+# NanoShare
+Quart-based file sharing service with a desktop CLI and folder sync client.
+
+## Python versions
+- **Server: Python 3.15+**, matching the `quart_common` submodule's minimum.
+  `.python-version` and the Docker image select Python 3.15.
+- **Standalone CLI: Python 3.14+**. Install with `uv tool install ./cli`.
+
+## Modern Python features
+- Native deferred annotations (Python 3.14, PEP 649/749) replace
+  `from __future__ import annotations` in application and CLI modules.
+- The CLI uses Python 3.14's `argparse` command typo suggestions.
+- Targeted `__lazy_modules__` declarations (Python 3.15, PEP 810) defer
+  command-specific CLI dependencies and QR/Pillow imports until needed.
+  Python 3.14 imports these normally. Server registration imports remain eager;
+  do not enable global lazy imports for the application.
+
+## Development and tests
+```bash
+uv sync --locked
+uv run --locked python -m pytest -q
+```
+
+The dev dependency group includes pytest, pytest-asyncio, and watchdog.
+The Docker build excludes this group with `--no-dev`.
+
+The complete suite includes `quart_common/tests` and requires Python 3.15.
+For standalone CLI checks on Python 3.14, use a separate environment:
+
+```bash
+uv venv --python 3.14 /tmp/nanoshare-cli-py314
+uv pip install --python /tmp/nanoshare-cli-py314/bin/python ./cli pytest
+/tmp/nanoshare-cli-py314/bin/python -m pytest -q tests/test_nanoshare_cli.py
+```
+
+Regression tests in `tests/test_python_features.py` cover deferred annotations,
+command suggestions, lazy help/completion imports, and QR rendering. Lazy import
+checks are skipped on Python 3.14.