docs: update README and v0.5.1 release notes

docs/RELEASE-NOTES.md

@@ -9,6 +9,23 @@ While v0.5.0 introduced the multi-user architecture, v0.5.1 strengthens the foun
 ---
 
 # Highlights
+## Runtime Efficiency (v0.5.1)
+
+| Metric              | Value      |
+|---------------------|------------|
+| Binary Size         | 11 MB      |
+| RSS Memory          | 11.8 MB    |
+| Peak RSS            | 11.8 MB    |
+| CPU Idle            | 0.02%      |
+| Swap Usage          | 0 KB       |
+| PIDs                | 7          |
+
+**On a typical 32 GB server:**
+- Memory usage: ~0.04%
+- No swapping
+- Plenty of headroom
+
+BZOD runs closer to a lightweight infrastructure service than a typical web application.
 
 ## Global Slug Registry