nvim,tmux,kitty: full config overhaul (AstroNvim → native 0.12)

Replaces AstroNvim v5 with from-scratch Neovim 0.12 config using
vim.lsp.config()/vim.lsp.enable() natively, lazy.nvim, blink.cmp,
and smart-splits tmux integration.

tmux: new C-Space prefix, hjkl pane nav, resize key table, tpm plugins.
kitty: add allow_remote_control for smart-splits.

dot_config/nvim/lua/options.lua

@@ -0,0 +1,62 @@
+local opt = vim.opt
+
+-- Line numbers
+opt.number = true
+opt.relativenumber = true
+opt.signcolumn = "yes"
+
+-- Indentation
+opt.tabstop = 4
+opt.shiftwidth = 4
+opt.expandtab = true
+opt.smartindent = true
+
+-- Editing
+opt.wrap = false
+opt.scrolloff = 8
+opt.sidescrolloff = 8
+opt.virtualedit = "block"
+opt.clipboard = "unnamedplus"
+
+-- Files
+opt.undofile = true
+opt.swapfile = false
+opt.backup = false
+
+-- Windows
+opt.splitright = true
+opt.splitbelow = true
+
+-- Search
+opt.ignorecase = true
+opt.smartcase = true
+opt.hlsearch = true
+opt.incsearch = true
+
+-- Performance
+opt.updatetime = 250
+opt.timeoutlen = 300
+
+-- Appearance
+opt.termguicolors = true
+opt.cursorline = true
+opt.showmode = false        -- lualine handles this
+opt.pumheight = 10
+opt.conceallevel = 2        -- for LaTeX/Markdown
+
+-- Folds (treesitter-based, foldenable=false = open all by default)
+opt.foldmethod = "expr"
+opt.foldexpr = "v:lua.vim.treesitter.foldexpr()"
+opt.foldenable = false
+opt.foldlevel = 99
+
+-- Spell (disabled globally; enabled per-filetype via ftplugin/)
+opt.spell = false
+
+-- Completion
+opt.completeopt = { "menu", "menuone", "noselect" }
+
+-- Misc
+opt.mouse = "a"
+opt.fileencoding = "utf-8"
+opt.shortmess:append("c")