docs: guard init.lua in CLAUDE.md; hide eob tilde markers

Add file placement rules to CLAUDE.md explicitly marking init.lua as
read-only upstream. Set fillchars.eob to hide end-of-buffer ~ characters.

Author: codemedic

CLAUDE.md

@@ -1,5 +1,16 @@
 # Neovim Config — Claude Instructions
 
+## File Placement Rules
+
+**`init.lua` is read-only upstream (kickstart.nvim).** You MUST NOT edit it under any circumstances. Doing so causes merge conflicts on upstream updates.
+
+All additions MUST go in one of:
+- `after/plugin/options.lua` — vim options and `vim.opt.*` settings
+- `after/plugin/keymaps.lua` — keymaps
+- `after/plugin/gui.lua` — GUI-specific settings
+- `lua/custom/plugins/<name>.lua` — plugin specs and overrides (Lazy.nvim merges these)
+- `lua/custom/` — general custom modules
+
 ## Keybinding Tips (`lua/custom/keytips.lua`)
 
 `keytips.lua` contains a **hand-curated static list** of keybinding tips shown at startup and via `:KeyTip`.

after/plugin/options.lua

@@ -7,6 +7,7 @@ vim.o.tabstop = 4 -- Number of spaces tabs count for
 vim.o.shiftwidth = 4 -- Size of an indent
 vim.o.smartindent = true -- Insert indents automatically
 vim.opt.spelllang = { 'en_gb' }
+vim.opt.fillchars = { eob = ' ' } -- hide end-of-buffer ~ markers
 
 -- Cursor — per-mode shapes with slow-typewriter blink (long on, brief off)
 vim.opt.guicursor = table.concat({