Capture back-face printing images for double-faced cards

Add a back_image_uri column to printings, populated during ingest from
a card's second card_faces image (only present for transform/MDFC/
reversible cards — split/adventure cards share one combined image and
correctly get ""). Plumb it through CardRef across every query path
(search, library, filters, deck contents) via the same printing row,
using a shared deterministic ORDER BY so front/back always come from
one printing.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

crates/mtgc-core/src/db.rs

@@ -21,12 +21,16 @@ const LIBRARY_MIGRATIONS: &[&str] = &[
 /// The attached alias under which the reference db is available at runtime.
 pub const REF_DB: &str = "ref";
 
-/// Correlated subquery selecting one image URL for the oracle card aliased `oc`.
-/// Returns NULL when no printing has an image. Read it as `Option<String>`.
-pub fn image_subquery() -> String {
+/// Correlated subquery selecting one column from the same printing (the first,
+/// by `rowid`, with a non-empty front image) for the oracle card aliased `oc`.
+/// Call once per desired column (e.g. `"image_uri"`, `"back_image_uri"`) — the
+/// shared `ORDER BY p.rowid` ensures they all resolve to the *same* printing
+/// row. Returns NULL when no printing has an image; read as `Option<String>`.
+pub fn image_subquery(column: &str) -> String {
     format!(
-        "(SELECT p.image_uri FROM {REF_DB}.printings p
-          WHERE p.oracle_id = oc.oracle_id AND p.image_uri <> '' LIMIT 1)"
+        "(SELECT p.{column} FROM {REF_DB}.printings p
+          WHERE p.oracle_id = oc.oracle_id AND p.image_uri <> ''
+          ORDER BY p.rowid LIMIT 1)"
     )
 }