Description

rtk json Cargo.toml fails with Failed to parse JSON / expected value at line 1 column 2. The error should indicate the file is not JSON.

Reproduction

rtk json Cargo.toml
# Error: Failed to parse JSON
# Caused by: expected value at line 1 column 2

Expected behavior

A clear error message like: Error: Cargo.toml is not a JSON file (detected TOML)

Suggestion

Detect file extension and suggest rtk deps for Cargo.toml or rtk read for other formats.