fix(ui): guard explorer selectors on slow networks

[rajatbeladiya]

Fixes the issue where clicking explorer selector buttons (e.g. +Metrics/+Params/+Images) immediately after page load on a slow network can lead to an error state.

Changes:

• Guard selector button click until selectFormData.options is available.
• Disable the selector button and show a "Loading…" tooltip when options aren't ready.
• Use safe defaults for suggestions to avoid undefined access during initial load.

Tested:

• Local Aim UI (aim up) with artificial fetch latency and verified selectors remain stable.
• npx eslint on modified files.

Closes #1574.

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