feat: add API key visibility toggle in Endpoint dashboard (#214)

- Added eye icon button to show/hide individual API keys
- Keys hidden by default on page load for security
- Copy button always copies full key regardless of visibility state
- Implemented per-key visibility state with React useState
- Added maskKey helper to display first 8 characters + "..."
- Clean up visibility state when keys are deleted

Improves security and UX when managing API keys in the dashboard.

CHANGELOG.md

@@ -1,3 +1,8 @@
+# Unreleased
+
+## Features
+- Added API key visibility toggle (eye icon) to Endpoint dashboard page for improved UX and security.
+
 # v0.2.66 (2026-02-06)
 
 ## Features