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/lazy.lua

@@ -27,7 +27,10 @@ require("lazy")
             change_detection = {
                 notify = false,
             },
+            ui = {
+                border = "rounded",
+            },
         })
 
 require("absolute.core.colorscheme")
-require("../current-theme");
+require("current-theme")