Error output ignores `--json` flag — should emit JSON envelope

Problem

When --json is passed and a command fails, errors are output as plain text to stderr instead of JSON:

$ dot --rpc wss://... query.AssetConversion.Pools --dump --json
Error: Unknown pallet "AssetConversion".

This breaks the --json contract — scripts cannot reliably parse error output.

Expected Behavior

When --json is passed, errors should also be valid JSON:

{"error": "Unknown pallet \"AssetConversion\""}

With the process still exiting non-zero so scripts can check $?.

Root Cause

handleError() in src/cli.ts always uses console.error() with plain text formatting, regardless of whether --json was passed. The error handler currently has no access to the parsed CLI options.

Suggested Fix

Store the --json/--output flag in a module-level variable (or lightweight process-level context) that handleError() can access. When JSON mode is active:

1. Emit {"error": "<message>"} to stdout (maintaining the contract that all JSON goes to stdout)
2. Keep the non-zero exit code
3. Optionally still log human-readable text to stderr for terminal users

Key Files

• src/cli.ts — handleError() error handler
• src/core/output.ts — output utilities

Start in src/cli.ts by tracing handleError() and how parsed CLI options are available, then read src/core/output.ts for existing output conventions. Verify that --json failures emit a JSON error envelope on stdout, preserve a non-zero exit code, and keep normal text behavior when JSON mode is not active.