fix(dedup): hash WAV fmt+data only, skipping render-varying metadata chunks

hashWavContent walks RIFF chunks and feeds only fmt body + data payload
through FNV-1a ('W' domain-separation prefix), skipping bext/iXML/LIST that
REAPER embeds with per-render origination timestamps. Fallback to whole-file
hashBytes for non-WAV. Wired into both capture commit paths.

Legacy entries keep their stored whole-file hash; a re-capture will not
collapse onto a pre-fix entry -- a one-time clean capture resolves it.

src/capture.cpp

@@ -499,15 +499,18 @@ CaptureResult OfflineRenderBackend::capture(const CaptureRequest& request) {
     s.lengthSeconds = request.endSeconds - request.startSeconds;
     s.captureTempo  = Master_GetTempo();   // BPM at capture time (verified ~4651)
     s.tier          = Tier::Scratch;       // captures land in scratch by default
-    // Content hash: FNV-1a over the rendered 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
+    // Content hash: WAV-aware FNV-1a over the rendered file's fmt+data chunks so
+    // hashReferencedElsewhere can identify copies in other banks and suppress the
+    // last-reference confirm when another bank still holds the same file. Using
+    // hashWavContent (not the raw hashBytes) skips render-varying metadata chunks
+    // (bext origination timestamp, iXML, LIST/INFO, etc.) so two renders of identical
+    // audio collapse to the same hash. Best-effort: an unreadable file leaves
     // contentHash empty — the safe, confirm-eliciting direction (bank_model treats
     // "" as non-participating in dedup, which is the existing fallback semantics).
     {
         const std::vector<std::uint8_t> fileBytes = readFileBytes(expectedPath);
         if (!fileBytes.empty()) {
-            s.contentHash = hashBytes(fileBytes.data(), fileBytes.size());
+            s.contentHash = hashWavContent(fileBytes);
         }
     }
     s.createdTimestamp = static_cast<std::int64_t>(std::time(nullptr));