Feature: Add Audio URL to CSV Export

The CSV export currently includes text, metadata, and match locations, but does not provide a direct link back to the original audio segment. Adding this would make the export far more useful for annotation, validation, and downstream processing.

**Proposal:**
Include a new column in the CSV output containing a URL or path to the original audio file associated with each result row.

**Why it’s useful:**
- Enables quick verification of matches.
- Supports research workflows that require re-listening to matched segments.

**Implementation notes:**
- Use the existing audio storage path/URL pattern in the DB.
- Consider adding both file-level link (raw audio), and time-coded link if supported (?t=start_sec).

Locate the CSV export entry point and inspect the existing audio storage path or URL pattern in the database. Add an audio link or path to each result row, then verify that exported rows include the expected link and, if supported, the time-coded start parameter.

Written by the indexing model from the issue text.