#3049 Docs: data query reference lists a --limit default of 100 and omits --single

The manual's data reference (content/manual/reference/data.md) is out of date for swamp data query.

What is wrong

1. --limit default. Two option tables, under ### swamp data query [predicate] and under ## Querying > ### Command, say --limit defaults to 100. The CLI has no default limit: the help text reads "Maximum results (unlimited when omitted)".
2. --single is missing from both option tables. It was added in swamp-club#2961 and is in the current release. The help text is "Require exactly one match; with --json, print the match (or its --select value) on its own instead of a results list". It conflicts with --limit, and it errors with QUERY_NO_MATCH or QUERY_MULTIPLE_MATCHES when anything other than one record matches.
3. What limited means. "Query Result Structure" and "Numeric Comparison" say limited is true when results were truncated by --limit. It is actually true whenever the page is full, that is, when the number of results equals the limit, even if no more records match. Since swamp-club#2985, a limited page counts only live records: catalog rows whose backing file is missing no longer use up a slot. --limit 0 returns no results with limited: true.

Suggested content

• In both option tables, change the --limit row to say "Maximum results (unlimited when omitted)".
• Add a --single row to both option tables, with a short --single --json example that shows the bare record or the selected value.
• Reword the limited description to: "true when the number of results reached --limit; more records may match".