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/flash.lua

@@ -0,0 +1,15 @@
+return {
+	enabled = false,
+	"folke/flash.nvim",
+	event = "VeryLazy",
+	---@type Flash.Config
+	opts = {},
+  -- stylua: ignore
+  keys = {
+    { "s", mode = { "n", "x", "o" }, function() require("flash").jump() end, desc = "Flash" },
+    { "S", mode = { "n", "x", "o" }, function() require("flash").treesitter() end, desc = "Flash Treesitter" },
+    { "r", mode = "o", function() require("flash").remote() end, desc = "Remote Flash" },
+    { "R", mode = { "o", "x" }, function() require("flash").treesitter_search() end, desc = "Treesitter Search" },
+    { "<c-s>", mode = { "c" }, function() require("flash").toggle() end, desc = "Toggle Flash Search" },
+  },
+}