feat: add plugins, formatting, and editor quality-of-life improvements

- Add leap.nvim (<CR> to jump, S for cross-window) with LeapBackdrop dimming
- Add mini.surround with default s-prefix keymaps
- Add conform.nvim with format-on-save and <leader>cf keymap
- Add undotree with <leader>uu toggle and nerd font shapes
- Add nvim-treesitter-context for sticky scope header (max 3 lines)
- Add inc-rename.nvim with Noice input dialog and <leader>cr keymap
- Add lazydev.nvim for proper Neovim Lua type definitions in lua_ls
- Enable Snacks modules: scratch, zen, terminal (<C-/> toggle), and expand picker with flash integration and frecency matcher
- Configure flash to suppress default keymaps (owned by leap/mini.surround)
- Switch gitsigns from numhl to signcolumn for Snacks.statuscolumn rendering
- Set 2-space indentation with expandtab
- Enable persistent undo via undofile
- Auto-restore persistence session on startup when no file args given

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lua/options.lua

@@ -7,14 +7,14 @@
 -- Autowrite/Autosave
 -- This ensures changes are saved on every buffer change or when leaving insert mode.
 vim.api.nvim_create_autocmd({ "InsertLeave", "TextChanged" }, {
-  group = vim.api.nvim_create_augroup("autosave", { clear = true }),
-  pattern = { "*" },
-  callback = function()
-    local buftype = vim.api.nvim_get_option_value("buftype", { buf = 0 })
-    if buftype == "" and vim.bo.modified then
-      vim.cmd("silent! update")
-    end
-  end,
+	group = vim.api.nvim_create_augroup("autosave", { clear = true }),
+	pattern = { "*" },
+	callback = function()
+		local buftype = vim.api.nvim_get_option_value("buftype", { buf = 0 })
+		if buftype == "" and vim.bo.modified then
+			vim.cmd("silent! update")
+		end
+	end,
 })
 
 -- Performance and UI defaults
@@ -22,3 +22,32 @@ vim.opt.updatetime = 200 -- Faster completion and CursorHold events
 vim.opt.autowrite = true -- Enable auto write
 vim.opt.number = true -- Show line numbers
 vim.opt.relativenumber = true -- Relative line numbers
+
+-- Persistent undo across sessions
+vim.opt.undofile = true
+
+-- Indentation
+vim.opt.tabstop = 2 -- Tab width in spaces
+vim.opt.shiftwidth = 2 -- Indent width for >> and auto-indent
+vim.opt.expandtab = true -- Use spaces instead of tabs
+
+-- FormatOnSave
+vim.api.nvim_create_autocmd("BufWritePre", {
+	pattern = "*",
+	callback = function(args)
+		require("conform").format({ bufnr = args.buf })
+	end,
+})
+
+-- Execute Format
+vim.api.nvim_create_user_command("Format", function(args)
+	local range = nil
+	if args.count ~= -1 then
+		local end_line = vim.api.nvim_buf_get_lines(0, args.line2 - 1, args.line2, true)[1]
+		range = {
+			start = { args.line1, 0 },
+			["end"] = { args.line2, end_line:len() },
+		}
+	end
+	require("conform").format({ async = true, lsp_format = "fallback", range = range })
+end, { range = true })