feat(nvim): phase 3 — replace nvim-cmp with blink.cmp and telescope with snacks.picker

Swap the completion engine to blink.cmp v1.x, dropping nvim-cmp,
its eight cmp-* sources, lspkind, and LuaSnip. Swap the picker
to snacks.picker, removing telescope.nvim and six telescope
extensions. LSP capabilities now sourced from blink.cmp; LSP
navigation keymaps and the colorscheme/keymaps/todo pickers move
to Snacks.picker. friendly-snippets is preserved as blink's
snippet source.

lua/absolute/after/blink-cmp.lua

@@ -0,0 +1,14 @@
+require("blink.cmp").setup({
+	keymap = { preset = "default" },
+	appearance = {
+		nerd_font_variant = "mono",
+	},
+	sources = {
+		default = { "lsp", "path", "snippets", "buffer" },
+	},
+	cmdline = {
+		keymap = { preset = "cmdline" },
+		completion = { menu = { auto_show = true } },
+	},
+	signature = { enabled = true },
+})