Thread title

Purpose: Let a thread's displayed title change after creation through an ordinary reply, with the authority, provenance and visibility of that change kept explicit. Scenario: The thread's author replies title: Clear name for this thread. The reply posts unchanged; because the author has authority and FORUM_TITLE_DIRECTIVE_ENABLED is on, the same commit adds an authored thread-subject record naming the reply and its bytes. Every title consumer now shows the new name and the root card's signals line reads Title set by <author>; on the thread page itself the heading, tab title and that line update in place when the accepted reply is rendered, without a reload. A later retraction or deletion of that reply withdraws the retitle and the previous title returns. An operator may retitle any thread; with FORUM_TITLE_DIRECTIVE_APPROVED_MEMBERS on, any approved member may. A reply by someone without authority, or with the flag off, stays plain text and changes nothing. Sources: record format, directive line (source unavailable), authority (source unavailable), precedence and withdrawal (source unavailable), write path (source unavailable), in-place root update (source unavailable), read-model columns. Boundary: Only thread roots have titles. System-fetched media titles still fill only an empty subject. Orphaned authored records after a source deletion are retained as history and have no effect. Suggestions from repliers without authority are not shown (recorded follow-up).