L7: capture-order slot model, card metadata overlay, tertiary-border selection

Add gap-preserving per-bank SlotMap (reorder + Alt-replace mutators, JSON
round-trip, insertion-order migration) to bank_book; stamp captureTimeSig on
Sample; pure card_meta formatters + card_drag gesture/slot module; card
metadata overlay + purple selection border in the panel. Shell drop/cursor
wiring deferred. Fixes: removeSample syncs SlotMap; card_drag gap-probe coordinate.

src/realtime_record.h

@@ -109,6 +109,10 @@ struct RecordedCapture {
     int    channelCount = 0;
     int    sampleRate   = 0;   // 0 when the project rate was unknown (as offline)
     double captureTempo = 0.0; // BPM at capture time (shell reads Master_GetTempo)
+    // Time signature at capture start (L7 F1; shell reads TimeMap_GetTimeSigAtTime).
+    // 0/0 = unstamped (matches the Sample default; formatter renders a blank read-out).
+    int    captureTimeSigNum   = 0;
+    int    captureTimeSigDenom = 0;
     std::int64_t createdTimestamp = 0;  // unix epoch seconds (shell reads the clock)
 };