refactor: simplify home-manager layout and fix terminal option drift

[derangga]

Summary

Cleanup pass over the nix-darwin config: one latent bug fix plus several structural simplifications. No behavior change on the current host beyond the intended ones.

Changes

Bug fix (terminal option drift)

• terminal.use was declared as an option in two independent module trees: nix-darwin (picks the Homebrew cask) and home-manager (picks the program config). Setting it on one side did not affect the other, so switching terminals could install the wrong cask. It is now a single terminal value set per host in flake.nix and passed to both sides. modules/terminal/options.nix deleted.

Layout

• Folded home/home.nix into modules/default.nix; the flake imports ./modules directly and no longer threads modulesDir through extraSpecialArgs. home/ removed.
• Standardized module entry files from config.nix to default.nix (aerospace, catppuccin, git, presenterm); imports now reference bare directories. sketchybar/nixvim untouched.

Simplification

• Catppuccin flavor set once globally instead of repeated per program via a cfg binding.
• Moved dev toolchains (bun, cargo, fnm, go, rustc, rust-analyzer) from environment.systemPackages to home.packages.
• Replaced ~60 hand-written per-language starship version overrides with the bundled no-runtime-versions preset. File renamed nosymbol.nix to no-version.nix.
• Enabled nix.optimise.automatic.

Docs

• Fixed CLAUDE.md and README hostname-vs-username drift, refreshed the structure tree, added a Mermaid architecture diagram, and updated the flake config example to include the required terminal field.