docs(ha-term-safety): fix mermaid sequenceDiagram parse error (semicolon in note)

Mermaid treats ';' as a statement separator, so 'Note over L: no callback;
barrier untouched' split mid-note and failed with a Parse error before 'end'.
Replaced the semicolon with a comma. Validated PARSE_OK via mermaid@11 parse().
The other ';' (config-bytes flowchart line) is inside a double-quoted node label,
which mermaid treats as a literal — valid, left unchanged.

.kiro/specs/ha-term-safety/design.md

@@ -192,7 +192,7 @@ sequenceDiagram
         A->>B: feed safe commit position into existing barrier
         Note over B: majority self-cap at durable_lsn + persist-before-ACK<br/>+ own-term writable gate (UNCHANGED)
     else held (prev-term / no quorum)
-        Note over L: no callback; barrier untouched
+        Note over L: no callback, barrier untouched
     end
     Note over A: committed config = latest WAL_CONFIG_MARKER<br/>within committed prefix (derived, not a separate index)
 ```