improve Stream Filters popover — auto-grow chip area and group chips by field

[arturminchukov]

1. Auto-grow chip area

The popover footer should grow vertically as chips are added, instead of clipping them into an 80px
scrollable strip.

• Replace the fixed FOOTER_HEIGHT = 80px with content-driven sizing on the chip footer.
• The popover should grow up to the viewport height; beyond that, scroll internally so it never
  overflows the screen.
• The top section (label list + values panel) keeps its current sizing — only the footer (chips) expands.

2. Group chips by field

When a field has multiple selected values, render a single chip group instead of N flat chips. Each
value keeps its own × button, and the whole group gets an additional × to remove the field entirely.