feat(home): theme CLI tools, add staples, env defaults and mime apps

- Catppuccin Mocha for fzf (colors), bat (catppuccin/bat tmTheme) and
  git delta (syntax-theme + navigate/line-numbers/side-by-side).
- CLI staples on every host: ripgrep, fd, jq, btop, plus gh (SSH) and
  tea (Gitea CLI).
- home.sessionVariables: PAGER, MANPAGER (bat), VISUAL; xdg.enable.
- xdg.mimeApps defaults (web->Firefox, directories->nemo).
- Document the stateVersion pin. README updated.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

statix.toml

@@ -0,0 +1,8 @@
+# statix lint config. Two default lints are disabled because they flag this
+# repo's intentional house style, not bugs:
+#   repeated_keys  - we use `foo.a = ...; foo.b = ...;` (dotted) over nesting.
+#   empty_pattern  - module files use `{ ... }:` / `{ }:` deliberately.
+disabled = [
+  "repeated_keys",
+  "empty_pattern",
+]