Filter with highlighting result

Description

• When using Filter, the table shows matched flows.
• It is hard to know exactly where the match is inside the selected flow.
• The app should highlight matched text in visible places, so users can find it quickly.

Current Problem

• Filter result only shows which flows are matched.
• After selecting a flow, users must manually search inside:
  • URL
  • Query
  • Request headers
  • Response headers
  • Cookies
  • Form data
  • Raw first line and headers
• This is slow when there are many rows or many headers.
• Body highlighting is too complex and should not be included for now.

Acceptance Criteria

• Highlight matched text only for the selected flow.
• Do not calculate highlights for all matched flows at once.
• Highlight matches in:
  • URL
  • Query
  • Request headers
  • Response headers
  • Cookies
  • Form data
  • Raw tab first line
  • Raw tab headers
• Do not highlight body content in Preview tab.
• Do not highlight body content in Raw tab.
• Highlight color must be readable in light mode and dark mode.
• Highlights must disappear when the filter is turned off.
• Highlights must disappear when there is no selected flow.
• Negative-only filters should not show highlights.
• Add unit tests for the highlight matching logic.