Migrate Neovim plugins from Packer to lazy.nvim

[akan72]

Summary

Branch 5: migrate Neovim plugin management from Packer → lazy.nvim.

• Replace Packer bootstrap with lazy.nvim bootstrap pinned to v11.17.5 (self-installs on first launch)
• Convert all use{} specs to lazy {} specs: run → build, requires → dependencies
• Set mapleader before lazy.setup so lazy keys specs bind correctly
• Add priority = 1000 (+ lazy = false) to the gruvbox colorscheme
• Remove the BufWritePost PackerCompile autocmd
• Lazy-load: telescope (keys + :Telescope), fugitive (:Git/:G + <leader>gs), markdown-preview (ft = markdown)
• Fix nvim-treesitter ensure_installed: "help" → "vimdoc" (parser renamed)
• Delete nvim/coc-settings.json (unused — config uses lsp-zero + Mason)
• Remove nvim/plugin/ from .gitignore (Packer artifact dir)
• assimilate.sh: drop the packer clone + PackerSync; lazy self-bootstraps and we trigger a headless Lazy! sync

Notes / deviations

• lsp.lua already used ts_ls (not tsserver), so the planned rename was a no-op.
• Kept the vim.tbl_flatten shim in init.lua. The plan lists removing it, but the still-pinned old plugin versions (e.g. telescope 0.1.1) reference vim.tbl_flatten, which is gone in nvim 0.11+. Removing the shim now would break them — it should be removed only after unpinning to newer versions (a later plan step). The shim is a no-op when unused, so keeping it is strictly safer.
• lazy-lock.json is not committed yet — it's generated on the first interactive launch. After merging: open nvim, let lazy install, run :Lazy to verify, then commit the lockfile.

Why & alternatives (from explanations.txt — Branch 5)

Change	Why	Alternatives
Migrate Packer → lazy.nvim	Packer archived since Aug 2023. lazy.nvim is the standard: lazy-lock.json (transitive pinning), lazy loading, built-in UI.	Stick with Packer (unmaintained, risk grows) or vim-plug (older).
Delete coc-settings.json	Config uses lsp-zero + Mason — CoC is a different framework. Dead file.	Keep if switching back to CoC (unlikely).
Keep/remove vim.tbl_flatten shim	Only needed for old pinned treesitter/telescope.	Kept as safety net until plugins are unpinned (harmless).
"help" → "vimdoc" parser	Treesitter renamed the parser; old name warns.	None — just a rename.
tsserver → ts_ls	mason-lspconfig renamed it.	Already ts_ls — no change needed.
Remove nvim/plugin/ from .gitignore	Packer artifact location; lazy doesn't use it.	None.
Update assimilate.sh (remove Packer clone)	lazy self-bootstraps from config.	Leave for now to roll back easily.
Add lazy-loading triggers	Faster startup — telescope on <C-p>, fugitive on :Git, etc.	Load everything eagerly (simpler, slower).

lazy-lock.json will be generated on first launch; commit it after verifying everything works locally.