Redesign plugins list and make plugin installation more flexible

[unocelli]

Summary

Introduces a dedicated plugins-list page with a FUXA-style card layout and updates the plugin installation flow to support a leaner default server setup.

What changed

• added a full-page plugins-list view with the same header structure used by apikeys-list
• replaced the previous list-style presentation with responsive plugin cards
• reused PluginService to install/remove plugins directly from the page
• added clearer visual states for installed, available, working, and disabled actions
• kept plugin ordering stable regardless of installed state
• refined the UI to a more compact layout consistent with FUXA

Installation model

• the server can now ship with only a small base set of plugins installed by default
• additional plugins are meant to be installed only when actually needed
• plugin installation is now more flexible than before, especially for modules with dependencies
• this makes module management easier in setups where plugin requirements vary by project or environment

Upgrade compatibility

• existing installations are not impacted by this change
• already installed plugins remain available after update
• plugins from existing installations are not expected to be uninstalled as part of this new approach
• this keeps upgrades safe while enabling a lighter default setup for new deployments

UI details

• compact cards with reduced padding and tighter vertical spacing
• improved action icons for Install and Remove
• clearer disabled state for unavailable actions
• intro panel updated with less rounded corners and larger text