fix: redirect debug/status output to stderr for json/xml output formats

[sridhar-3009]

Problem

Closes #568.

When probe is called with --format=json (e.g. via the MCP symbols tool), debug lines like Pattern: ..., Path: ..., and Falling back to BM25 ranking... were written to stdout before the JSON result. Any JSON parser downstream received:

Pattern: symbols
Path: '/tmp/...'
Options: Reranker: bm25
Using BM25 ranking (Okapi BM25 algorithm)
{"results": [], ...}

And failed with: Unexpected token 'P', "Pattern: s"... is not valid JSON

Fix

src/main.rs — wrap the Pattern: and Path: println! blocks in a format guard so they are only printed for text output:

if params.format != "json" && params.format != "xml" {
    println!("{} {}", "Pattern:".bold().green(), params.pattern);
}

src/search/result_ranking.rs — change "Falling back to BM25 ranking..." and related debug println! calls to eprintln!.

src/ranking.rs — same for SIMD debug messages.

All status/diagnostic output now goes to stderr, leaving stdout clean JSON for downstream parsers.

[buger]

Yep, makes sense! Thank you!