Fix: Local source filtering

[mugetau]

The local source didn't use any metadata from ComicInfo.xml (or the legacy details.json) when browsing/searching. Only the folder name was searchable, so tags like genre, author, artist, and publishing status were effectively write-only.

This adds:

• New filters in the local source's filter sheet: Author, Artist, and Genre (free-text, genre supports comma-separated terms matched with AND logic), and Status (dropdown matching the six ComicInfo publishing statuses).
• The existing search box now also matches against author, artist, description, and genre pulled from metadata, not just the folder name.

Metadata is parsed from each manga's top-level ComicInfo.xml, falling back to the legacy details.json if that's what a given manga folder has (read in parallel across the library, and only when a filter/query is actually active, so plain browsing with no filters is unaffected performance-wise).

For visibility: I'm aware of #437, which tackles this alongside broader indexing/performance work. This PR is a narrower, immediately mergeable fix for the search/filter bug specifically (#397), not a replacement for that effort.

Closes #397

Testing / self-review

• Tested against a local library in the emulator with manga folders containing ComicInfo.xml files covering different genres/authors/status values; confirmed each filter narrows results correctly, and that they combine (e.g. genre + status together).
• Self-reviewed the diff.
• No new UI was introduced. The new filters reuse the existing Filter.Text/Filter.Select components already used by other sources, so they render through the app's existing filter sheet and pick up theming/tablet layout for free. Nothing to check there beyond confirming the sheet still displays correctly, which it does.