fix(appellate): Tweaks ACMSPageHandler to handle firefox load - #422

Summary

Fixes ACMS page observer to handle Firefox page load timing and make sure observer is active for HTMX updates.

The existing ACMSPageHandler logic had a conditional that would skip observer creation if indexContent or fullDocketContent elements were already present on the page. This behavior worked in Chrome, where the extension typically loads before HTMX incrementally adds content, but broke in Firefox, where the page often finishes loading before the extension runs.

In Firefox this resulted in:

• When content was already present, handleAcmsDocket() would run but no observer was created
• Without an observer, subsequent HTMX partial updates were not detected
• RECAP failing to respond to dynamic content changes after initial load

key changes:

• Restructured the logic to always create the observer (if one does not already exist)
• Preserved the immediate handleAcmsDocket() call for already-loaded content
• Adds singleton pattern to prevent duplicate observers if ACMSPageHandler is called multiple times