Add native LSP diagnostics workflow

[foundev]

Summary

• add native LSP client support for configured language servers
• expose install-default /setup lsp controls for read/write diagnostics and server management
• add a diagnostics tool and append diagnostics after successful write/edit operations, with read diagnostics opt-in

Verification

• cargo fmt --check
• cargo clippy --all-targets -- -D warnings
• cargo build --release
• cargo test (full pass outside sandbox: 1041 passed, 2 ignored)
• focused unit tests for /setup lsp and diagnostics tool metadata/schema