[anthonyportugal]

Adds the development stack (TypeScript/Node, Go, Tauri) to the opt-in dev layer and GPU monitoring for hybrid laptops. Merge without squash to keep the commits.

Changes

• dev base tools – direnv (hooked into zsh), xh, hyperfine and oha, all from the official repositories.
• dev-go feature – go, golangci-lint, delve. Go 1.21+ fetches project toolchains itself, so no version manager.
• dev-tauri feature – rustup and the Tauri v2 system libraries (webkit2gtk-4.1, libayatana-appindicator, ...). rustup conflicts with the rust package; the README explains the switch.
• dev-herdr feature – herdr-bin from AUR (the upstream release binary with a pinned sha256). It is a feature so the base dev layer still installs with --backend pacman.
• cli – nvtop, and a second GPU box in btop so Intel + NVIDIA laptops show both.

Review notes

• Breaking changes: none. New features are opt-in; the help text, completions and both READMEs list them.
• Plan tests match package names exactly (a substring check let go pass on golangci-lint).

Testing

• tests/smoke.sh and shellcheck -x pass locally on the final commit.
• Each package addition was checked RED → GREEN in tests/optional-layers-smoke.sh / tests/cli-tools-smoke.sh.