fix(tui): show all plugins with correct per-project install state

[bojanrajkovic]

Summary

• The CLI returns all installed plugins globally but hides them from the available array if they're installed anywhere — so plugins installed in other projects became invisible
• processAvailablePlugin unconditionally merged installed data from all projects, making available plugins appear as "installed, disabled" in the wrong project
• Replaces the filter-based approach with per-plugin relevance checks via isInstalledInProject:
  • Installed in current project → shown with correct scope and enabled/disabled state
  • Installed at user scope → shown with user scope and state
  • Installed elsewhere or only available → shown without install state (available for installation)

🤖 Generated with Claude Code

[bojanrajkovic]

Test plan

• Run cpm from a project with plugins installed at project scope — verify those plugins show as installed with correct scope and enabled/disabled
• Run cpm from a different project — verify those same plugins appear but without install state (no scope, no enabled/disabled)
• Verify user-scoped plugins appear correctly everywhere with their scope and state
• Verify plugins only in the available list show as not installed
• Verify plugins the CLI hides from available (because they're installed elsewhere) still appear in the list
• mise run ci — all checks pass