fix: property inspector - read sample rate from node.latency, not node.rate

- node.rate was a PipeWire internal flag (always 1), not sample rate
- Now reads from node.latency (format: '256/48000') for quantum + rate
- Fallback to clock.rate if latency not available
- Reuses rate field for ALSA period-size
- Shows 'Latency: 256 samples @ 48000 Hz' and 'Period Size: 256'

frontend/src/components/GraphCanvas.svelte

@@ -693,8 +693,8 @@
             {#if nd.sample_rate > 0}<tr><td class="pk">Sample Rate</td><td>{nd.sample_rate} Hz</td></tr>{/if}
             {#if nd.channels > 0}<tr><td class="pk">Channels</td><td>{nd.channels}</td></tr>{/if}
             {#if nd.format}<tr><td class="pk">Format</td><td>{nd.format}</td></tr>{/if}
-            {#if nd.quantum > 0}<tr><td class="pk">Quantum</td><td>{nd.quantum}</td></tr>{/if}
-            {#if nd.rate > 0}<tr><td class="pk">Rate</td><td>{nd.rate}</td></tr>{/if}
+            {#if nd.quantum > 0}<tr><td class="pk">Latency</td><td>{nd.quantum} samples @ {nd.sample_rate} Hz</td></tr>{/if}
+            {#if nd.rate > 0}<tr><td class="pk">Period Size</td><td>{nd.rate}</td></tr>{/if}
             {#if nd.device_name}<tr><td class="pk">Device</td><td>{nd.device_name}</td></tr>{/if}
             {#if nd.device_bus}<tr><td class="pk">Bus</td><td>{nd.device_bus}</td></tr>{/if}
             {#if nd.api}<tr><td class="pk">API</td><td>{nd.api}</td></tr>{/if}