Fix file recipe: replace Markdown downloads that now 404

[claudespice]

What the recipe said

file/README.md Step 1 of the Query Markdown Documents walkthrough downloads four docs pages:

files=(
  "clickhouse.md"
  "databricks.md"
  "debezium.md"
  "delta-lake.md"
)
for file in "${files[@]}"; do
  curl -O "$base_url/$file"
done

What actually happens

databricks and delta-lake are now directories in spiceai/docs (website/docs/components/data-connectors/), not flat .md files, so those two URLs 404. Because the script uses curl -O without -f, the 404 body is written to disk instead of failing — the reader silently ends up with two junk files:

$ for f in clickhouse.md databricks.md debezium.md delta-lake.md; do curl -sO "$base_url/$f"; done
$ ls -l *.md | awk '{print $5, $9}'
8088 clickhouse.md
14 databricks.md
17917 debezium.md
14 delta-lake.md

$ cat databricks.md
404: Not Found

The dataset still loads with 4 rows, so Step 4's output looks right — but two of the four "documents" contain the string 404: Not Found, which quietly defeats the point of the recipe.

What changed

Swapped the two dead entries for ducklake.md and iceberg.md — both still flat .md files in the same directory, and both keep the lakehouse-connector flavour of the originals. Updated the Step 4 expected output to match.

Verified all four download real content:

clickhouse.md      8088 bytes  --- title: 'ClickHouse Data Connector' …
debezium.md       17917 bytes  --- title: 'Debezium Data Connector' …
ducklake.md        8161 bytes  --- title: 'DuckLake Data Connector' …
iceberg.md        19050 bytes  --- title: 'Iceberg Data Connector' …

Checked against current stable Spice v2.1.1. The download step is confirmed by running it; the spice run / spice sql steps were not re-run (no CLI in the audit environment), but nothing about them changes — only the four filenames do.

Note for reviewers: adding -f (or --fail) to the curl would make a future breakage loud instead of silent. Left out here to keep the diff to the actual drift, happy to add it if wanted.