Add `[[hide-dir]]` rule to remove entire directories when their
condition evaluates to true, extending the existing file-level
hide functionality to directory trees.

Add `!=` operator support in rule expressions and ensure the entire
expression is consumed during parsing, invalidating any trailing
garbage tokens that would previously be silently ignored.

Support `[[user.toggle-mutex]]` groups in rule.toml to enforce
mutually exclusive toggle options, and derive `program_crate_name`
from `program_name` using snake_case conversion.

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.