export: support external plugin drivers (CSV/JSON)

[danielnuld]

Problem

export_query_to_file (the Export as CSV/JSON action in the SQL editor) only
supports the built-in drivers — stream_to_sink matches mysql/postgres/sqlite
and returns Unsupported driver for export: <id> for every external plugin driver.
So users on plugin-backed connections (e.g. the IBM Informix plugin) can't export.

Change

Adds a fallback branch for plugin drivers in src-tauri/src/export.rs: it looks
up the registered driver via registry::get_driver and pages through the driver's
own execute_query (1000 rows/page), forwarding every row to the existing
RowSink (CSV or JSON). Built-in drivers are untouched and still stream directly.

other => stream_query_via_plugin(other, params, query, &mut on_row).await,

The loop stops when a page returns no rows or pagination.has_more is false
(falling back to "fewer than a full page" when a driver doesn't report pagination),
so non-SELECT statements terminate immediately. Progress/cancellation are handled
by the existing on_row closure, so the cancel button and progress modal keep
working for plugins too.

Notes

• No change to the public command surface or the built-in code paths.
• I wasn't able to run a full local cargo check here — the openssl-sys
  vendored build needs perl, which isn't available in my shell (unrelated to
  this change). The patch mirrors the existing built-in dispatch and the driver
  trait signature exactly; CI should confirm the build.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (1 file)

• src-tauri/src/export.rs

---

_{Reviewed by kimi-k2.7-code-20260612 · Input: 60.5K · Output: 9.6K · Cached: 915.5K}