fix(capture): populate contentHash on captured samples to fix always-prompting remove

contentHash was left empty on every capture; hashReferencedElsewhere returns
false for empty hashes, so every remove looked like a last reference. Add
FNV-1a hashBytes to capture_paths, wire into both commit paths. NOTE: this
activates index dedup-by-hash in production — a bit-identical re-capture now
collapses onto the existing entry instead of adding a duplicate (spec-intended).

src/capture_realtime.cpp

@@ -78,7 +78,7 @@
 #include <string>
 #include <vector>
 
-#include "capture_paths.h"
+#include "capture_paths.h"   // hashBytes, deriveBankPaths
 #include "peaks.h"           // lastFrameAboveThreshold, AudioSample
 #include "realtime_record.h"
 #include "render_settings.h" // autoTrimEndRatio, realtimeRecordWindowEnd
@@ -512,6 +512,19 @@ CaptureResult finalizeRecording(RealtimeCaptureState& st) {
     result.status  = CaptureStatus::Ok;
     result.sample  = sampleFromRecordedCapture(cap);
 
+    // Content hash: FNV-1a over the (possibly trimmed) bank file bytes so
+    // hashReferencedElsewhere can identify copies in other banks and suppress the
+    // last-reference confirm when another bank still holds the same file.
+    // Best-effort: an unreadable file leaves contentHash empty — the safe,
+    // confirm-eliciting direction (bank_model treats "" as non-participating).
+    {
+        const std::vector<std::uint8_t> fileBytes = readAllBytes(destPath);
+        if (!fileBytes.empty()) {
+            result.sample.contentHash =
+                hashBytes(fileBytes.data(), fileBytes.size());
+        }
+    }
+
     // The recorded file's true length differs from the request range when a tail was
     // recorded, so the Sample length must reflect the FILE, not the range:
     //   Auto with a trim applied -> the trimmed length trimAutoTailInPlace returned.