feat(builtins): add tomlq builtin (jq-style TOML query and transform)

[chaliy]

Goal

Add first-class TOML processing without introducing a second major query language.

Proposal

Implement a native tomlq builtin with jq-style semantics:

• parse TOML input/file into structured data
• run existing jq/jaq-style filters against that data model
• emit JSON by default
• optional round-trip back to TOML for write/update workflows

Why this shape

Bashkit already has strong jq support. Reusing the jq mental model is lower-friction than adopting a separate TOML-specific DSL.

Initial scope

• tomlq FILTER [FILE]
• stdin support
• -r raw output
• -c compact JSON output
• -t / --toml-output to render result back as TOML when possible
• good errors for non-representable TOML values / invalid top-level output

Non-goals

• shelling out to external tools
• adding a large independent TOML CLI surface before validating demand

Implementation sketch

• parse via Rust TOML crate
• convert TOML -> JSON-like value for filter execution
• optionally convert filtered result back to TOML for output
• spec tests for read, select, update, stdin, invalid TOML, invalid round-trip cases

[chaliy]

Resolved in PR #585 or #588