Add safe Neovim configuration reload command

[Unique-Divine]

Goal

Allow the non-plugin parts of this Neovim configuration to be reloaded without
closing and restarting Neovim.

Provide a user command, proposed as :ConfigReload, that safely reapplies the
supported configuration files without attempting to re-run Lazy.nvim startup.

Background

Running command :source $MYVIMRC re-executes file nvim/init.lua. That file
calls function require("lazy").setup(...), and Lazy.nvim intentionally rejects
a second setup pass with:

Re-sourcing your config is not supported with lazy.nvim

Lazy.nvim supports command :Lazy reload {plugin} for individual plugins, but
that experimental command does not reload this repository's core configuration.

The desired workflow is:

1. Edit and save a supported Neovim config file.
2. Run command :ConfigReload.
3. Observe the change without restarting Neovim.

Terminology

An autocommand is Neovim behavior triggered by an event, such as saving a
buffer or opening a file type.

An augroup is a named collection of autocommands. Creating an augroup with
clear = true removes its previous autocommands before adding replacements.
This prevents reloads from stacking duplicate actions, such as formatting the
same file multiple times after saving.

Proposed design

• Keep Lazy.nvim bootstrap and function require("lazy").setup(...) as
  startup-only behavior in file nvim/init.lua.
• Refactor reloadable configuration into modules with an idempotent setup()
  function. Running setup() multiple times must leave one effective version
  of each keymap, command, option, and autocommand.
• Add command :ConfigReload, implemented outside the Lazy.nvim setup path.
• Have command :ConfigReload reload only an explicit allowlist of safe core
  modules. Do not source file nvim/init.lua.
• Clear and recreate reloadable autocommands through named augroups.
• Define reloadable user commands with force = true, or otherwise avoid
  redefining them during a reload.
• Print a concise confirmation listing the modules that were reloaded.

Initial reloadable candidates

• File nvim/lua/core/vim.lua

  • Core options and keymaps.
  • Requires cleanup before it can be safely re-run because it defines user
    commands and has ungrouped FileType autocommands.

• File nvim/lua/core/telescope.lua

  • Telescope setup and keymaps.

• File nvim/lua/core/treesitter.lua

  • Already clears its UserTreesitter augroup and is a strong candidate.

• File nvim/lua/core/cmp.lua

  • Completion setup.

• File nvim/lua/core/comment.lua

  • Comment.nvim and context-commentstring setup.

• File nvim/lua/core/harpoon.lua

  • Harpoon keymaps.

Excluded from the first implementation

• File nvim/init.lua: must not be re-run because it initializes Lazy.nvim.
• File nvim/lua/core/lazy-plugins.lua: contributes Lazy.nvim plugin specs.
• File nvim/lua/core/lsp.lua: reconfigures LSP/Mason state and defines user
  commands; evaluate separately.
• File nvim/lua/core/fmt.lua: its ungrouped BufWritePost autocommand would
  duplicate save-time formatting.
• Files nvim/lua/core/debugger.lua,
  nvim/lua/core/debug-kickstart.lua, and nvim/lua/core/snippets.lua:
  plugin state requires separate idempotency review.

Acceptance criteria

• Command :ConfigReload exists and does not call
  require("lazy").setup(...).
• Running :ConfigReload twice produces no errors or duplicate behavior.
• Reloading does not show Lazy.nvim's re-sourcing warning.
• Reloadable autocommands belong to named augroups that are cleared before
  replacement.
• Reloadable user commands can be redefined without errors.
• Existing terminal keymap <Esc><Esc> still enters terminal-normal mode.
• Existing keymap <leader>r still runs command :checktime.
• The configuration documents which files :ConfigReload covers and which
  changes still require a Neovim restart.
• Add a headless Neovim test or equivalent reproducible check that loads
  the reloadable configuration twice.

Non-goals

• Reloading Lazy.nvim itself.
• Installing, updating, or reloading arbitrary plugins.
• Restarting active language servers unless a later follow-up explicitly adds
  that behavior.