Rework library sync around a JSON document; add card filters

Sync

The previous design put the merge inside SQL: timestamp-stamping triggers,
a tombstone table, per-device SQLite snapshots, a device id in the database,
and row merges written as correlated-subquery UPDATEs. All of that schema
was inherited by desktop, and the merge was very hard to verify.

Replace it with a single JSON document plus a three-way merge in plain Rust.
Storing the last-read remote document as the merge base makes "who changed
what" and "what was deleted" derivable, which removes the tombstone table,
the updated_at columns and all eight triggers. It also makes a single shared
file safe: if a publish is lost the remote is unchanged, so the next merge
re-detects the local edits and republishes rather than reading their absence
as a deletion. That removes the need for per-device files and for device
identity entirely. Schema impact drops to one column, decks.uuid.

Conflicts resolve to "theirs", which is required for convergence rather than
chosen for taste — preferring ours has each device re-asserting its own value
forever. Every such choice is reported to the user.

SQLite becomes invisible: the working copy lives in the app data dir and the
user only ever names a .json file. There is always a document, defaulting to
private storage, so edits are never stranded with nowhere to be saved.
Pointing at a file that doesn't exist yet moves the current library there;
pointing at one that does adopts it. A converter brings a pre-document
library.db across.

Android reaches the folder through the Storage Access Framework rather than
MANAGE_EXTERNAL_STORAGE, so no storage permission is declared at all.

Filters

Track card origin in reference.db: Universes Beyond, digital-only and
Un-set cards, plus numeric power/toughness. Each origin flag is derived as
"every printing", not "any printing" — ordinary cards get reprinted into
those sets, and Lightning Bolt appearing in Marvel Commander must not hide
it. Non-numeric power ("*", "1+*") stays NULL so it drops out of range
filters instead of being compared as zero.

Also wire up filters over data already present: price range, format legality
(restricted counts as legal) and "can be a commander". All of these degrade
silently against an older reference.db rather than failing every query.

The shared criteria live in one component used by both filter panels, as a
compact row of icon toggles.

Card Search gains the Library tab's bulk selection: checkboxes in both views,
select-all, and a bulk add-to-deck with a single undo for the whole batch.

src-tauri/src/lib.rs

@@ -1,5 +1,6 @@
 mod commands;
 mod state;
+mod sync;
 
 use std::sync::Mutex;
 
@@ -31,10 +32,27 @@ pub(crate) fn logged<T>(what: &str, result: Result<T, String>) -> Result<T, Stri
     result
 }
 
+/// Register the Kotlin-side `SyncPlugin` and stash its handle in app state, so
+/// the sync commands can call across to SAF. See `sync.rs` for why library sync
+/// goes through a Java plugin rather than plain `std::fs`.
+#[cfg(target_os = "android")]
+fn sync_plugin() -> tauri::plugin::TauriPlugin<tauri::Wry> {
+    tauri::plugin::Builder::new("mtgc-sync")
+        .setup(|app, api| {
+            let handle = api.register_android_plugin("com.garrettmills.mtgc", "SyncPlugin")?;
+            app.manage(sync::SyncBridge(handle));
+            Ok(())
+        })
+        .build()
+}
+
 #[cfg_attr(mobile, tauri::mobile_entry_point)]
 pub fn run() {
-    tauri::Builder::default()
-        .plugin(tauri_plugin_dialog::init())
+    let builder = tauri::Builder::default().plugin(tauri_plugin_dialog::init());
+    #[cfg(target_os = "android")]
+    let builder = builder.plugin(sync_plugin());
+
+    builder
         .setup(|app| {
             let data_dir = app
                 .path()
@@ -47,10 +65,15 @@ pub fn run() {
         })
         .invoke_handler(tauri::generate_handler![
             commands::get_status,
-            commands::set_library_path,
             commands::update_card_data,
             commands::cancel_update_card_data,
             commands::import_reference_db,
+            sync::sync_status,
+            sync::sync_pick_folder,
+            sync::sync_set_document,
+            sync::sync_forget_document,
+            sync::sync_now,
+            sync::convert_legacy_library,
             commands::search_cards,
             commands::add_owned,
             commands::set_owned,