Include line in --json search output

Problem

The CLI formatter includes line numbers in search results (e.g. qmd://blog/notebook/database_vector.qmd:2), but the --json formatter omits them. The line number is computed from chunkPos via extractSnippet in the CLI path (cli/qmd.js:1562) but isn't passed through to searchResultsToJson in formatter.js.

This makes it harder to build editor integrations. For example, VS Code's code --goto file:line works great with the CLI output, but parsing coloured terminal output is fragile. A --json workflow like:

qmd query "vector database" --json | jq -r '.[0] | "\(.file):\(.line)"' | xargs code --goto

would be much more robust, but currently .line is absent from the JSON.

Suggested fix

In cli/formatter.js, searchResultsToJson (around line 53), the result object is built as:

return {
    docid: `#${row.docid}`,
    score: Math.round(row.score * 100) / 100,
    file: row.displayPath,
    title: row.title,
    ...(row.context && { context: row.context }),
    ...(body && { body }),
    ...(snippet && { snippet }),
};

Adding the line number would be something like:

const { line, snippet: snip } = extractSnippet(bodyStr, query, 300, row.chunkPos, undefined, opts.intent);
return {
    docid: `#${row.docid}`,
    score: Math.round(row.score * 100) / 100,
    file: row.displayPath,
    line,
    title: row.title,
    ...(row.context && { context: row.context }),
    ...(body && { body }),
    ...(snip && !opts.full && { snippet: snip }),
};

The extractSnippet function is already imported in qmd.js; it may need to be made available to formatter.js as well, or the line could be pre-computed and passed through on the result object.

Use case

Building shell/editor integrations that open search results at the matching line — VS Code (code --goto), Vim (:e +line file), Emacs, etc.