app: add flagged page with list sorted by flagged date

Patch for sorting a list of flagged packages by flagged date.

• Replace top navigation menu item "Flagging" with "Flagged" that links to a /flagged page. Add "Flagged" top navigation menu item that links to a /flagged page, rename /flagging link to "How to flag"
• The list is sorted in descending order, most recently flagged first.
• Display new version in a new column without needing to hover a cursor over the current version to view for each row.
• Remove unused columns, e.g. license, branch and architecture.
  • License seems less important in the scope of flagged packages. Project URL is retained for users to potentially visit upstream websites to confirm the new version information.
  • Branch is edge only, and the dropdown menu selection shows the branch name. Not sure if it is useful to filter by other branches, as packages outdated on edge will also be outdated on other branches.
  • Package filter still allows limiting by architecture, but only one architecture is displayed at a time to deduplicate listings, not really needed if already printed in the filter selection.
• Filtering is set to origin=yes as subpackages are duplicate entries of the origin package.

Closes #2 (closed)

Preview (updated 2025-02-26):