fix(capture): warn 300–799px PNG floor; hard-block only below 300

Split FLOOR_WARN_PX=800 / FLOOR_BLOCK_PX=300. Warn-band still encodes and
includes the photo (Photos-ready + batchApply ok+warn). Block excludes
siblings and clean cal. CAPTURE-105 / CAPTURE.md / PHOTOS.md updated.

frontend/src/App.svelte

@@ -77,12 +77,14 @@
       widthMinIn: eighthsToIn(r.widths.min),
       widthMaxIn: eighthsToIn(r.widths.max),
       widthAvgIn: eighthsToIn(r.widths.avg),
-      sourceBelowFloor: r.sourceBelowFloor,
+      sourceBelowBlock: r.sourceBelowBlock,
+      sourceBelowWarn: r.sourceBelowWarn,
       lineup: buildPhotosReadyLineup({
         inventoryPng: r.inventoryPng,
         overlayPng: r.overlayPng,
         batchApply: m.batchApply,
-        sourceBelowFloor: r.sourceBelowFloor,
+        sourceBelowBlock: r.sourceBelowBlock,
+        sourceBelowWarn: r.sourceBelowWarn,
       }),
     };
     saving = true;