fix: order posts by their modification columns

[chubes4]

What

post_modified and post_modified_gmt are missing from the posts order allowlist, so any query ordered by them fails closed in the native executor with unsupported_order.

WP_Query emits ORDER BY wp_posts.post_modified for orderby=modified — the default for recently-updated listings, including the WordPress admin post list.

Why it is worth a fix rather than a workaround

get_posts() turns a backend query failure into an empty array. The caller cannot tell "no matching posts" from "this backend refused the query."

Found on a site with 663 wiki articles where wp intelligence wiki list reported No wiki articles. The rows were present the whole time, and the same query ordered by post_date returned them immediately:

post_date        -> 3 posts
post_modified    -> 0 posts  ERR: mdi-native cannot apply the requested ordering collation.
post_title       -> 3 posts
menu_order       -> 3 posts

Change

Add post_modified and post_modified_gmt to order_columns in the posts schema. Both are datetimes in the generated core catalog and sort through the same comparator already used for post_date and post_date_gmt, so this widens the allowlist without introducing a new ordering path.

Tests

Extends tests/smoke-native-core-schema-catalog.php to pin every core datetime column WP_Query orders by. Verified it discriminates:

• With the source change reverted and the test kept: FAIL: posts order by every core datetime column WP_Query emits
• With the fix: PASS, 9/9 checks in that file

Known gap, not addressed here

post_name is also absent from the allowlist, so orderby=name has the same silent-empty behavior. Left out of this PR because slug ordering has an ASCII-collation question the datetime columns do not.

Separately: the smoke suite prints FAIL: lines while exiting 0, so homeboy.json's php "$test_file" || exit 1 runner reports green on a failing test. 17 files currently fail this way on main. Worth its own issue.

AI assistance: GPT-6 Astra via OpenCode, under Chris Huber direction, traced the empty wiki listing to the order allowlist, made the change, and wrote the regression. Chris Huber remains responsible for review.