docs: update README to match current config layout and tooling

[RWejlgaard]

The README had drifted from the actual repo. This brings it back in sync.

What changed

• Neovim: documented lazy.nvim (was Packer), nvim-tree (was Neo-tree), nvim-cmp without Copilot, fugitive + gitsigns, and the Mason LSP set (bash, docker, go, json, yaml, python, lua).
• Fish: prompt is now simple.fish + history-sync.fish (was Tide). config.fish was split into aliases.fish and functions.fish (deployed to conf.d/); documented each.
• Tmux: described the modular status bar (status.sh + status.conf gadgets) and the Bluetooth popup (prefix + b); plugins are tpm + tmux-better-mouse-mode.
• Packages: added eza & lazygit, dropped npm; documented Fedora/RHEL and Gentoo support.
• Added a repository layout section and a note on make refresh.
• Fixed Manual Setup paths to point at the config/ tree and use symlinks.