fix(config): enable documentation mode only explicitly

ConfigEOS.documentation_mode() was true as soon as Sphinx was imported
anywhere in the process. A test importing Sphinx therefore switched all
later tests into documentation mode, and test_config_md_current failed
depending on test order. Documentation mode is now enabled only by the
documentation generators (_force_documentation_mode) or by the Sphinx
configuration, which sets sys._called_from_sphinx in docs/conf.py.

Declare _force_documentation_mode as a ClassVar. Without the annotation
pydantic turned it into a private attribute, and the class attribute was
a truthy descriptor object.

Behavior change: because of that descriptor, every running EOS was in
documentation mode, so the get_adapter/config/measurement/prediction/ems/
database/resource_registry() guards never raised "access before init" and
created the singletons lazily on first access. They now raise for every
access before initialization. The worker process of uvicorn's auto-reload
(server.reload, make run-dev) relied on that: the app's lifespan now sets up
the configuration and initializes the singletons that do not exist yet.

Leave runtime state out of the documentation: the Home Assistant entity ID
properties and OptimizationCommonSettings.keys return an empty list in
documentation mode, so entity IDs and solution keys of a running system
no longer reach the generated configuration docs.

Keep the tests isolated: test_doc sets documentation mode on the class
and test_docstringrst restores sys._called_from_sphinx after reading the
Sphinx configuration. Add tests for how documentation mode is enabled and
for the runtime values it leaves out.

Additional changes
- Generate openapi.json in documentation mode, as the config docs.
- Share the documentation mode check as coreabc.documentation_mode().
- Move the logging and server address setup of run_eos() to setup_eos_config().
- Test that EOS starts with server.reload.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/akkudoktoreos/core/coreabc.py

@@ -106,6 +106,31 @@ class AdapterMixin:
         return get_adapter()
 
 
+def documentation_mode() -> bool:
+    """Return whether EOS runs in documentation mode.
+
+    Shortcut for ``ConfigEOS.documentation_mode()`` for modules that cannot
+    import ``ConfigEOS`` at module level. Documentation shows no runtime state,
+    e.g. entity IDs of a Home Assistant instance or keys of an optimization
+    solution.
+
+    Returns:
+        True if the documentation is being generated.
+    """
+    from akkudoktoreos.config.config import ConfigEOS
+
+    return ConfigEOS.documentation_mode()
+
+
+def config_initialized() -> bool:
+    """Return whether the configuration singleton exists, without creating it.
+
+    Returns:
+        True if ``get_config(init=...)`` already created the configuration.
+    """
+    return _config_eos is not None
+
+
 def get_config(init: Union[bool, dict[str, bool]] = False) -> ConfigEOS:
     """Retrieve the singleton EOS configuration instance.