Add the `class-add` command to create project classes from
templates registered in `.mling/classes.toml`. Supports name
derivation (snake_case, PascalCase, etc.), template expansion,
and shell completions.

Add `--pair` flag to output config values as `"key" = "value"` pairs,
and provide escaped formatting for display. Move config path resolution
to a helper function and expose the underlying hash map for rendering
and completion.

Add a new `cfg` command to view and edit configuration
items stored as key-value pairs in a JSON file.

Implement `mling proj-init` to generate projects from zip templates with
checklist-based configuration. Extracts template archive, moves
checklist for user editing, and expands `tmpl_`-prefixed files using
`just_template` with boolean rule evaluation from `rule.toml` for file
hides and display toggles.

Add `pkg-show` to display installed packages and their versions,
removing its NOT_IMPL marker from help. Include internal commands
to load enabled package paths and completion scripts.

Add package enable/disable functionality with version matching
for pkg-enable, and fix help text to reflect implemented commands.

Implement `mling uninstall` to remove installed packages by name or
name@version, with shell completion support. Rework install to build
release binaries, copy them plus completion scripts to a per-version
directory under the user data dir.