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/after/gitsigns.lua

@@ -1,3 +1,10 @@
 local gitsigns = require("gitsigns")
 
-gitsigns.setup()
+gitsigns.setup({
+	current_line_blame = true,
+	current_line_blame_opts = {
+		virt_text_pos = "eol",
+		delay = 500,
+		ignore_whitespace = false,
+	},
+})