docs: add lock file support

[bug-ops]

Summary

• Update extension description to mention lock file support
• Add Lock File Support to features list
• Update Supported Files table with lock files for each ecosystem

Changes

extension.toml:

• Updated description: "Dependency management LSP with lock file support for Cargo.toml, package.json, pyproject.toml"

README.md:

• Added Lock File Support feature
• Updated table to show lock files (Cargo.lock, package-lock.json, poetry.lock, uv.lock)
• Changed Python status from "Planned" to supported