fix(api-explorer): restore Base URL editing for single-server API specs

[DanPiazza-Netwrix]

Summary

• The swizzled Server component only rendered the URL field when options.length > 1, leaving the edit panel completely empty for APIs with a single server URL (e.g. Change Tracker). Clicking Edit showed nothing but a Done button.
• Added a swizzled slice.ts with a new setCustomServerUrl action that sets state.value.url directly without requiring a match in state.options, enabling free-form URL editing.
• Replaced the conditional options.length > 1 select with a FormTextInput (using local draft state) for single-option APIs; dispatches setCustomServerUrl on Done.
• Guarded the stale-URL reset so custom URLs aren't overwritten on re-render (reset only runs when options.length > 1).
• Reset to default is now always visible (was previously only shown when server variables were present).
• Added type="button" to both Reset and Done buttons — without it, pressing Enter in the URL field triggered Reset to default (browser default-submit behavior).

Test plan

• Navigate to an API reference page with a single server URL (e.g. /docs/changetracker/8_1/api/reference/acknowledge-events-get)
• Hover over Base URL — Edit button appears
• Click Edit — URL text input is shown pre-filled with the current URL
• Type a new URL — field accepts input without resetting
• Press Enter — form stays open (does not reset)
• Click Done — form closes and Base URL display updates to the new value
• Click Edit again → click Reset to default — URL reverts to the original spec URL
• Restart dev server and repeat — setCustomServerUrl is fully wired and URL persists to Redux (used in API request calls)

Note: Full Redux persistence of the custom URL requires a dev server restart after this PR is merged, as rspack must re-resolve the @theme/ApiExplorer/Server/slice alias to the new swizzled file.

Generated with AI

Co-Authored-By: Claude Code ai@netwrix.com