Domain selection dropdown overflows and lacks filtering with many domains

[ithsjeff]

shlink-web-client version

4.7.0

How do you use shlink-web-client

https://app.shlink.io

Current behavior

• UI Obstruction: The list of 10+ domains (e.g., qris.art, qris.to, tautan.store) expands so far down that it hides the "Extra checks" and "Configure behavior" cards.
• Navigation Fatigue: As the domain list grows, the time-to-select increases linearly because there is no way to type-to-filter.

Expected behavior

• Searchable Select: Implementing a searchable dropdown (like react-select or similar) would allow a user to type "qris" and instantly see only relevant options.
• Sticky Positioning: The dropdown should intelligently position itself (above or below the input) based on available screen real estate without overlapping critical action buttons like "Save."

Minimum steps to reproduce

1. Add multiple domains: Configure 10 or more custom domains in the Shlink instance.
2. Open Creation Form: Navigate to the "Create short URL" page in the web client.
3. Trigger Dropdown: Click the "Domain" selection box.

[acelaya]

There's a couple improvements I want to make here.

Generally for dropdowns:

1. Make sure all dropdowns are always rendered inside the viewport. If they need to overlap the anchor component, so be it.
   Right now they always render above or below the anchor component, wherever there's more space, but there might be cases where neither one of them has enough space, like in the screenshot you shared.
2. If they are still bigger than the viewport, shrink them and add their own scrolling, or at least make them affect the general scroll so that you can still scroll the page.

For this component in particular:

1. Reconsider the dual component. Perhaps it would be better to have a regular text box but with autocomplete, where you can either select an existing domain or add a new one. Similar to the tags component, but with the option to select only one value.
   However, for this particular case you might want to see the dropdown right away, not after you start typing, so I need to think about this.
2. If the dual component is preserved because previous point is not as usable, then I'll add a search box in the dropdown itself when selecting an existing domain.