Add fzf-lua for project navigation

Wraps the fzf binary already installed via brew, alongside rg and fd,
so it needs no plugin dependencies - unlike telescope, which would
also pull in plenary. Picks up nvim-web-devicons for file icons, which
is the first thing actually using that plugin.

Maps live under <leader>f: files, live grep, buffers, grep the word
under the cursor, and help tags. The intent is to stop treating netrw
as the way into a project and switch to jumping by name, leaving
buffers open and bouncing between them, rather than quitting out of
nvim to change file.

Netrw is untouched and still on :Ex for browsing an unfamiliar tree.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

neovim/nvim-pack-lock.json

@@ -1,5 +1,9 @@
 {
   "plugins": {
+    "fzf-lua": {
+      "rev": "8671012a7b2a1648595952c655039d51fb301c14",
+      "src": "https://github.com/ibhagwan/fzf-lua"
+    },
     "gitsigns.nvim": {
       "rev": "31d6fb2d618bca1482b9f274751ead5f03461408",
       "src": "https://github.com/lewis6991/gitsigns.nvim"