Add PSKReporter style filters to POTA, SOTA, WWFF and WWBOTA

[alanhargreaves]

What does this PR do?

• Adds PSKReporter style filters to POTA, SOTA, WWFF and WWBOTA. These filters are persistent across reloads. Similar to PSKReporter, the filters button (magnifying glass) will show the number of filters active if it is more than 0.
• Adds the filter and callsign toggle buttons to the panels in Modern Layout
• Tidies up the buttons to use the new Icon code and lays them out similarly to PSKReporter

Type of change

• Bug fix
• New feature
• Performance improvement
• Refactor / code cleanup
• Documentation
• Translation
• Map layer plugin

How to test

Go to any of the POTA, SOTA, WWFF or WWBOTA panels

1. Verify that you see the filter, label and world map buttons
2. Verify that you can add and remove filters
3. Verify that you can toggle callsign display
4. Verify that you can toggle whether or not the spots are reflected on the map at all

Checklist

• App loads without console errors
• Tested in Dark, Light, and Retro themes
• Responsive at different screen sizes (desktop + mobile)
• If touching server.js: caches have TTLs and size caps (we serve 2,000+ concurrent users)
• If adding an API route: includes caching and error handling
• If adding a panel: wired into Modern, Classic, and Dockable layouts
• No hardcoded colors — uses CSS variables (var(--accent-cyan), etc.)
• No .bak, .old, console.log debug lines, or test scripts included

See Issues

• [FEATURE] Hunter Filters #23
• [FEATURE] Ability to add filters for POTA #322
• [FEATURE] #432