Fix import dialog showing 0 notes/media for subdeck-only decks

[fabiomanz]

Summary

Fixes #190. The import dialog's "Notes:" and "Media Files:" counts were read directly from the top-level JSON arrays, so decks whose notes/media live only in subdecks displayed 0.

This matches the approach proposed in the issue: do the JSON→Deck conversion once, before showing the dialog, and let the dialog ask the Deck for the counts. This removes a coupling between the dialog and the on-disk JSON layout.

Changes

• Deck: new get_media_file_count() parallel to the existing get_note_count(), plus a media_files field.
• deck_initializer.from_json: populate deck.media_files from the JSON before post_import_filter strips the key.
• anki_importer.load_deck: build the Deck up front and pass it to the dialog instead of the raw JSON.
• ImportDialog: takes a Deck; note models are read from deck.metadata.models; counts come from the two get_*_count() methods.

Tests

• test/representation/deck_spec.py (new) — unit tests for both count methods (flat, nested, subdeck-only).
• test/representation/deck_initializer_spec.py — added an integration test verifying from_json populates media_files recursively.

Manual verification

Tested locally in Anki by importing a deck whose notes live only in a subdeck — the dialog now reports the correct counts instead of 0.

[aplaice]

Thanks very much for this! (And thanks for patiently rebasing over master, multiple times...)

I'm sorry for the horrible delay replying and also for the multiple issues with our actions!

One slight issue is that it seems that if the same media files are present in multiple sub-decks (e.g. re-using the same media in multiple notes or having shared (_xxx) media) then I think we'll get an overcount. (Manual testing seems to confirm this.) (FWIW I think that using 'file' as the universal media filename in _make_deck, in the deck_spec test is an oversimplification, since if the filename is the same we should only really report a single media file.)

Otherwise, this looks great!

[fabiomanz]

Thanks for the feedback. Can you please take a look if the newest changes fulfill your questions?

[aplaice]

Thanks very much!