bug: audit --output json for stdout pollution in piped contexts

Problem

When piping polkadot-cli query ... --output json into jq or other JSON consumers, users have reported getting parse errors due to non-JSON output mixed into stdout. This makes the CLI unreliable in scripted/piped contexts.

Analysis

Code analysis shows printResult in src/core/output.ts produces valid JSON arrays. The Spinner is not used in the query path. The user may have hit this on an older version, but it's worth a thorough audit to prevent regressions.

Proposed Solution

Audit all stdout writes across all commands to ensure that when --output json is active, only printResult writes to stdout. Specifically:

1. Grep for all console.log, process.stdout.write, and Bun.write(Bun.stdout, ...) calls
2. Ensure spinner output, progress messages, and any informational text go to stderr when --output json is set
3. Add a pipe-mode integration test that validates command --output json | jq . succeeds for representative queries

Priority

HIGH — this is the most annoying friction point reported by users.

Files to audit

• src/core/output.ts
• src/commands/query.ts
• src/commands/inspect.ts
• Any command file that writes to stdout

Start by reading src/core/output.ts, src/commands/query.ts, and src/commands/inspect.ts, then grep the repository for console.log, process.stdout.write, and Bun.write(Bun.stdout, ...). Audit stdout behavior when --output json is active and add a pipe-mode integration test for representative queries. Done means JSON consumers such as jq receive only valid JSON, with informational output routed to stderr.