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+.

cli/nanoshare_client/app.py

@@ -1,13 +1,8 @@
-from __future__ import annotations
-
 import os
 import sys
 from pathlib import Path
 
-try:
-  import tomllib
-except ImportError:  # pragma: no cover
-  tomllib = None
+import tomllib
 
 from .config import DEFAULT_CONFIG
 from .http_client import NanoShareClient
@@ -24,7 +19,7 @@ def parse_registry_env(value: str) -> dict[str, str]:
   return registry
 
 def load_config(path: str | os.PathLike | None) -> dict:
-  if not path or tomllib is None:
+  if not path:
     return {}
   config_path = Path(path).expanduser()
   if not config_path.is_file():