Fix CLI crash when Plex is disabled in config

[bin101]

Summary

• Loading a config where plex.enabled is explicitly false still forced Plex username/password mode, causing a login attempt with empty credentials and a plexapi.exceptions.BadRequest.
• The resulting error dialog then crashed with RuntimeError: asyncio.run() cannot be called from a running event loop, because the console's message dialog called the synchronous Application.run() from inside the already-running event loop.
• While testing the flow above, the console's language selection step crashed with AttributeError: property 'language' of 'OrganizerStore' object has no setter — the setter function was named set_language instead of language, so the @language.setter decorator bound to the wrong name and the property stayed read-only.
• Finishing a run without Plex enabled crashed with KeyError: 'new_show' and never wrote the config, because isinstance(extra_fields.get("new_show", False), int) is True for the default False value (bool is a subclass of int in Python), causing an attempt to delete a key that was never set.

Fixes #23

Changes

• src/organizer.py: respect the actual boolean value of plex.enabled instead of only checking its presence.
• src/console.py: make _message_dialog async and use run_async(), matching the existing _input_dialog and GUI implementations.
• src/store.py: rename the language property setter function from set_language to language so it actually attaches to the property.
• src/console.py: exclude bool in the new_show int check in start_process()'s finally block so the sentinel/default values don't trigger a bogus key deletion.

Test plan

• Verified py_compile passes for all changed files
• Load a config with plex.enabled: false (no top-level mode) in console mode and confirm it starts in .nfo/Jellyfin mode without attempting a Plex login
• Confirm existing configs with plex.enabled: true / valid mode still go through the Plex login flow unchanged
• Trigger a Plex error path and confirm the error dialog displays instead of crashing with the asyncio RuntimeError
• Run through the console "advanced settings" language selection step and confirm no AttributeError is raised
• Complete a full console run without Plex enabled and confirm the config file is written without a KeyError