Adopt shellactions submodule and re-add Go/Rust toolchain setup

[jerrod-storm]

Context

The shared composite actions that previously lived in shellops/actions/ (envrc, git-config, setup) have been replaced by kernelle-soft/shellactions -- a repo of portable CI bash scripts.

The Go/Rust toolchain setup that was in shellops/actions/setup/action.yaml was deleted because it's a consumer concern.

Tasks

1. Add shellactions as a submodule at shell/actions:

   git submodule add <forgejo>/kernelle-soft/shellactions.git shell/actions

2. Re-add Go/Rust toolchain setup locally (inline in workflows or as a local script):

   • Go: actions/setup-go@v5
   • Rust: dtolnay/rust-toolchain@master + Swatinem/rust-cache@v2
   • cargo-binstall: cargo-bins/cargo-binstall@main

3. Update workflows to use shell/actions/setup, shell/actions/git-config, etc. instead of ./shell/.shock/actions/envrc and ./shell/.shock/actions/git-config

4. Update submodule path from shell/.shock to shell/.ops (shellops rename)

Blocked by

Kaitos migration to Forgejo Actions