feat: plugin manager integration — complement lazy.nvim, packer, vim-plug UIs

[mbadran]

Problem

Plugin managers (lazy.nvim, packer.nvim, vim-plug) show installation status but not contribution status — you can see that fugitive is installed but not what commands it adds. headlights shows contributions but not installation metadata. There's a gap.

Proposed integration

lazy.nvim

• Read require("lazy").plugins() for all plugin specs
• Cross-reference with headlights bundles by dir field
• For each bundle, show: version, last update date, load time (ms), load trigger (cmd/ft/event/manual)
• Add a "lazy info" entry in the category list: Info [loaded: 12ms / trigger: cmd]
• From headlights UI, pressing <CR> on Info opens :Lazy <plugin-name>

packer.nvim

• Read _G.packer_plugins for install status and config

vim-plug

• Read g:plugs dict

UI additions

Each bundle entry in the popup shows an indicator:

  fugitive          [15 cmds  8 maps]  ●loaded
  some-lazy-plugin  [cmd: SomeCmd]     ○unloaded

Config

require("headlights").setup({
  show_manager_info = true,   -- show load time, trigger, etc.
  show_unloaded     = true,   -- show unloaded lazy plugins
})

Acceptance criteria

• lazy.nvim: load time, trigger, and version shown per bundle
• Unloaded plugins appear (links to feat: show unloaded plugins via plugin manager metadata and filesystem fallback #30 — filesystem/registry issue)
• show_manager_info config option
• Works gracefully when no supported plugin manager is detected

References

• PRD.md — F-16, F-17