feat(nvim): phase 1 — triage and abandoned-plugin cleanup

Fix keymap collision on <leader>j/<leader>k (now resize-only;
location-list moved to ]l/[l). Migrate diagnostic signs from
deprecated vim.fn.sign_define to vim.diagnostic.config. Drop
orphan after/nvim-tree.lua and the bogus require("../current-theme").
Add foundation snacks.nvim spec. Remove playground, vim-maximizer,
poet-v, git-blame, render-markdown, and all five AI plugin specs.
Enable gitsigns current_line_blame.

lua/absolute/plugins/venv-selector.lua

@@ -1,11 +1,10 @@
 return {
 	"linux-cultist/venv-selector.nvim",
 	lazy = false,
-	branch = "regexp", -- This is the regexp branch, use this for the new version
+	branch = "main", -- This is the regexp branch, use this for the new version
 	dependencies = {
 		"neovim/nvim-lspconfig",
 		"nvim-telescope/telescope.nvim",
-		"mfussenegger/nvim-dap-python",
 	},
 	config = function()
 		require("absolute.after.venv-selector")