nixvim: expand keymaps and snacks picker integration

- Add mkExpr helper and use it for j/k screen-line movement
- Add native LSP keymaps (gd, grr, gri, grt, grn, gra, gO) alongside Glance previews (gD, gR, gM, gY)
- Add Trouble toggles for qflist, loclist, symbols, LSP panes
- Add quickfix/loclist navigation (]q/[q/]l/[l)
- Add alternate file shortcuts (<leader><leader>, <leader>w-)
- Add Snacks picker keymaps for LSP symbols, registers, jumps, qflist, loclist
- Add opts (jumpoptions=stack, switchbuf) to programs.nixvim
- Integrate Trouble into Snacks picker via <C-t> action
- Minor formatting cleanup in snacks.nix

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

modules/home/nixvim/plugins/editor/snacks.nix

@@ -1,9 +1,26 @@
-{ pkgs, ... }: {
+{pkgs, ...}: {
   programs.nixvim = {
-    extraPlugins = [ pkgs.vimPlugins.snacks-nvim ];
+    extraPlugins = [pkgs.vimPlugins.snacks-nvim];
+
     extraConfigLua = ''
       require("snacks").setup({
-        picker   = { enabled = true },
+        picker = {
+          enabled = true,
+
+          actions = require("trouble.sources.snacks").actions,
+
+          win = {
+            input = {
+              keys = {
+                ["<C-t>"] = {
+                  "trouble_open",
+                  mode = { "n", "i" },
+                },
+              },
+            },
+          },
+        },
+
         notifier = { enabled = true },
         words    = { enabled = true },
         scroll   = { enabled = true },