Sync with upstream kickstart.nvim: adopt vim.pack

[ThbltLmr]

Summary

• Adopts upstream kickstart.nvim's migration from lazy.nvim to vim.pack (Neovim 0.12's built-in package manager, upstream PR Refactor/vim.pack nvim-lua/kickstart.nvim#2005).
• Re-applies all local customizations on top of the new structure: 9 custom plugins, 6 LSP servers, conform prettier-vs-biome logic, neo-tree tweaks, custom keymaps, PHP .. → -> abbreviation.
• Branch was built from upstream/master directly (not a 69-commit replay rebase) to avoid pervasive conflicts on every commit that touched init.lua. Backup of the previous master is preserved on origin/backup/pre-upstream-sync-20260519.

What changed

Commit	Scope
30d05ff	Port 9 custom plugins to per-file vim.pack specs in lua/custom/plugins/ (typr, nvim-ts-autotag, trouble, oil, catppuccin, hardtime, markdown-preview, lazygit, harpoon)
8e02885	neo-tree: reveal right + show hidden/gitignored
5a3a92c	init.lua: <leader>tc/<leader>yp/<leader>yP/<leader>gb keymaps, PHP FileType autocmd, 6 LSP servers (gopls, rust_analyzer, ts_ls, cssls, phpactor, prismals), prettier/biome per-buffer conform logic, enable kickstart.plugins.{debug,indent_line,lint,autopairs,neo-tree} + custom.plugins loader
bb88a98	Disable markdownlint by default (honors prior local 6bc02fc disable md lint)

Test plan

• Headless boot installs every plugin without errors
• :checkhealth passes (no fatal errors; only pre-existing environment warnings)
• All 9 custom keymaps register (<leader>tc, <leader>mp, <leader>MP, -, <leader>h, <leader>lg, <leader>xx, <leader>yp, <leader>gb)
• catppuccin-frappe colorscheme override applied
• nvim-ts-autotag, oil, trouble, hardtime, harpoon modules load
• Open markdown buffer attaches treesitter highlights without errors
• Interactive smoke test: open nvim, exercise keymaps, :LazyGit, <leader>xx, :Mason, format-on-save in a project with .prettierrc
• Confirm gopls, rust_analyzer, ts_ls attach when opening a Go/Rust/TS file

Merging note

This PR diverges from master (70 ahead, 69 behind) because it was built from upstream/master rather than replayed onto local history. The GitHub "Merge" button will conflict everywhere — the intended merge path is locally:

```bash
git checkout master
git reset --hard feature/upstream-sync-vimpack
git push --force-with-lease origin master
```

Rollback

If anything breaks: roll master back to `backup/pre-upstream-sync-20260519` (already pushed to origin).