fix(docs): restore v0.8.2 performance note

Problem\nThe v0.8.2 performance note was incorrectly folded into the changelog flow, which left the performance index pointing at v0.8.0 as the current version.\n\nImplementation\nRestore docs/performance/v0.8.2.md as a standalone performance note, update the performance index to mark v0.8.2 as current, and add the page back to the MkDocs performance navigation alongside the v0.8.2 release note.\n\nTests\npython -m mkdocs build --clean\n\nNotes\nThe changelog v0.8.2 release note remains separate from the performance note by design.

Author: sentomk

docs/performance/index.md

@@ -4,21 +4,19 @@ This section tracks performance-oriented algorithm evolution by version.
 
 ---
 
-## Current Standalone Algorithm Note
+## Current Version
 
-**v0.8.0** is the current standalone algorithm note.
+**v0.8.2** is the current performance baseline.
 
-- [Open v0.8.0 details](v0.8.0.md)
-
-## Latest Release Note
-
-- [v0.8.2 release note](../changelog/v0.8.2.md)
+- [Open v0.8.2 performance note](v0.8.2.md)
+- [Open v0.8.2 release note](../changelog/v0.8.2.md)
 
 ---
 
 ## Version Index
 
-- [v0.8.0](v0.8.0.md) (standalone algorithm note)
+- [v0.8.2](v0.8.2.md) (current)
+- [v0.8.0](v0.8.0.md) (baseline)
 
 ---