Fix health check with lazy.nvim, handle null playlists, preserve C-p for navigation

[rosscondie]

Hey Trash sick plugin, thanks for building it I heard about it on the podcast btw.

It wasn't working out of the box with LazyVim for me, so I dug in a bit and noticed a couple of small issues. Also added C-p for navigation again as it collided with Telescope's default for previous, happy to drop that part if it's too much but the null check and health check fixes would be useful I think.

1. Fix health check discovery when plugin is lazy-loaded

README lazy.nvim example used cmd = { "Jam" } and lazy=true even with LazyVim.defaults.lazy=false. lua/jam/health.lua stays off &rtp until :Jam loads, so :checkhealth jam shows No healthcheck found for every LazyVim user following the docs (while :Jam health works). Removed cmd from docs so :checkhealth jam is discoverable eagerly.

2. Handle null playlist items returned by Spotify search

GET /search?q=Beatles&type=playlist returns [null,null,{...}] for restricted playlists -> vim.NIL (truthy) -> providers/spotify.lua:51 normalize crashes attempt to index userdata. Guarded normalize and all buckets (search, album_tracks, artist_top_tracks, show_episodes, playlist_items, now_playing) to skip vim.NIL. Unfiltered Beatles now OK 56 vs crash before.

3. Preserve C-p for navigation and remap pause to M-p

ui/picker.lua mapped <C-p> -> pause, shadowing telescope/mappings.lua:145 C-p = move_selection_previous. Normal vim users expect C-p/C-n to move. Remapped pause to <M-p> (Alt-p) in both pickers and updated README.md/doc/jam.txt. Requires Option as Alt in Kitty/WezTerm/iTerm on macOS.