Fix relationship name-to-post resolution

[sirreal]

Three bugs in lib/class-relationships.php broke the name→slug→post-ID resolution that builds p2p connections:

1. names_to_slugs() never detects fully qualified names. strpos( '\\', $name ) has haystack and needle swapped, so $fully_qualified is always false and a \-prefixed call is still resolved against the current namespace first. PHP semantics say a fully qualified name resolves only globally; now it does. This deliberately changes candidate order for \-qualified calls made inside a namespace.

2. get_ids_for_slugs() connects every matching scope. The loop says "stop searching the chain" but uses continue, so when both the namespace-scoped and the global candidate resolve to posts, both are connected — duplicate/spurious p2p connections. Now the first (most specific) match wins.

3. An empty slug map connects items to post ID 1. When no posts of a target type were imported, the raw array-of-candidate-arrays was left in $relationships, and the connection loop's intval( array, 10 ) coerces each to 1 — connecting items to whatever post has ID 1. The candidates are now cleared so nothing reaches the connection loop. This is the TODO why might this be empty? test class-IXR.php spot.

The new tests fail on master (3 of 5; the other two pin existing correct behavior) and pass with the fix; the full suite passes.

Observed while here, left alone: the methods branches of the connection loop pass 'data' => current_time( 'mysql' ) where the functions branches pass 'date' => — looks like a typo, but changing stored p2p meta is out of scope for this fix.

Found by the multi-agent review during #262; extracted as a standalone change.

🤖 Generated with Claude Code