Feat: Articles using kit infoboxes — the embeddedin reach tile (T433621, MR 4/4)

Fourth stacked T433621 MR, on !161 (merged). Tile 7 — articles transcluding kit-imported infoboxes — in three commits:

1. The embeddedin scanner (items per (wiki, template) from import-template-success events; by-anyone reach with exclusions riding on the importer; never-delete on removed transclusions).
2. Change tags on all items (the tags column, sentinel-delimited whole-tag matching, NULL = not captured vs "||" = captured-none; usercontribs + getPageCreator gain tags at zero extra request cost).
3. The origin refinement (task, decided 2026-08-01): items are dated by the revision that INTRODUCED the transclusion — revisions walk bounded at the import timestamp, parse&oldid&prop=templates per candidate, linear (exact, first addition) below a threshold and bisect (documented approximation) above; insert-only-once-resolved with the origin revision's tags; template identity by PAGE ID (rename/redirect-proof); per-(wiki, template) cursor + per-subject budget so a big template cannot monopolise a pass; unresolvable pages retry. Windows truthfully and tag-bearing like every other tile — no discovery-time rows ever ship.

Verified: fixture smokes for all of the above (bounded walk, linear-vs-bisect economy, RevDeleted retry, budget/cursor resume, page-id identity, tags semantics, idempotency) + lint/build.