fix: align table separator style in secrets-management.md

Resolves markdownlint MD060 errors by spacing the secret store reference
table separator to match the rest of the table.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: djsauble

docs/concepts/secrets-management.md

@@ -186,7 +186,7 @@ active with the old secret value.
 ## Secret store reference
 
 | Store | Primary auth | Retrieval command |
-|---|---|---|
+| --- | --- | --- |
 | macOS Keychain | Login session / biometric | `security find-generic-password -a "$USER" -s "name" -w` |
 | Linux keyring | Desktop session | `secret-tool lookup service name account user` |
 | 1Password | `op signin` / biometric | `op read op://vault/item/field` |