Add flash.nvim, vim-visual-multi, and buffer completion source

- Add flash.nvim for fast screen navigation (s/S keymaps)
- Add vim-visual-multi for multiple cursor support
- Add buffer words as a blink.cmp completion source

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

init.lua

@@ -790,7 +790,7 @@ require('lazy').setup({
       },
 
       sources = {
-        default = { 'lsp', 'path', 'snippets' },
+        default = { 'lsp', 'path', 'snippets', 'buffer' },
       },
 
       snippets = { preset = 'luasnip' },

lua/custom/plugins/init.lua

@@ -13,6 +13,18 @@ return {
     },
   },
   { 'editorconfig/editorconfig-vim' },
+  {
+    'folke/flash.nvim',
+    event = 'VeryLazy',
+    keys = {
+      { 's', function() require('flash').jump() end, mode = { 'n', 'x', 'o' }, desc = 'Flash jump' },
+      { 'S', function() require('flash').treesitter() end, mode = { 'n', 'x', 'o' }, desc = 'Flash treesitter' },
+    },
+  },
+  {
+    'mg979/vim-visual-multi',
+    event = 'VeryLazy',
+  },
   {
     'akinsho/toggleterm.nvim',
     version = '*',