Add CLI diagnostics checker

[ViTeXFTW]

Summary

• add zerosyntax-lsp check for one-shot diagnostics from files, directories, or stdin
• share workspace, BIG archive, W3D, and string-table scanning between the CLI and LSP backend
• support stable human/JSON output, severity-based exit codes, base roots, and cross-file indexing
• document CLI usage and output contracts

Why

A batch diagnostics interface enables LLM edit/check loops, CI and pre-commit validation, mod build gates, and reproducible checks without launching an editor or speaking LSP.

Validation

• cargo test --locked
• cargo fmt --all --check
• cargo clippy --locked --all-targets --all-features -- -D warnings
• python crates/server/tests/e2e.py target/debug/zerosyntax-lsp.exe

The CLI integration suite runs the real binary and covers stdin, JSON/human output, Unicode positions, failure thresholds, directory deduplication, cross-file resolution, directory and .big base roots, and invalid usage.

[greptile-apps]

Greptile Summary

This PR adds one-shot command-line diagnostics to zerosyntax-lsp. The main changes are:

• New zerosyntax-lsp check subcommand for files, directories, and stdin.
• Shared scanning for workspace INIs, BIG archives, W3D assets, and string tables.
• Human and JSON diagnostic output with severity-based exit codes.
• Documentation for CLI usage, output shape, and exit-code behavior.

Confidence Score: 5/5

Safe to merge with minimal risk.

The changed paths are cohesive and covered by focused CLI integration tests for the main workflows.

No files require special attention.

T-Rex Logs

What T-Rex did

• T-Rex executed the requested contract verification for the pull request.
• T-Rex confirmed that local artifact references were not uploaded with the verification results.
• T-Rex documented the missing artifacts and prepared a note for reviewers to upload or supply references.

_{Ran code and verified through T-Rex}

Important Files Changed

Filename	Overview
crates/server/src/cli.rs	Implements the diagnostics CLI, including target/base scanning, stdin support, output formats, and failure thresholds.
crates/server/src/scan.rs	Extracts shared filesystem, BIG archive, W3D, and string-table scanning with checked variants for CLI use.
crates/server/src/main.rs	Routes non-LSP invocations into the CLI while preserving default and --stdio LSP startup.
crates/server/src/backend.rs	Refactors backend scanning to use the shared scanner while keeping workspace indexing and virtual BIG file behavior.
crates/server/tests/cli.rs	Adds integration coverage for stdin, JSON/human output, thresholds, deduplication, base roots, and usage failures.
docs/language-server.md	Documents command-line diagnostics usage, JSON fields, severity thresholds, and exit codes.

_{Reviews (2): Last reviewed commit: "accept stdio transport flag" | Re-trigger Greptile}

[ViTeXFTW]

@greptileai