docs(showcase): fold this pass's defects into the shared conventions

Seven conventions every future piece inherits, each from a defect in
this pass that no existing budget could see: a band is hooped onto its
host and never set flush against it; a member is tenoned into its seat
and never stood on it, measured against the host read off the mesh;
posts go under a roof's corners, with the corners taken from the pooled
eave vertices rather than one fascia board; a roof is sized from what
it covers, not from what carries it; the subject hangs where it can be
seen; mirrored assemblies pair and compare, with the falsifier sized
inside BBOX_TOL; and segment counts are a silhouette budget.

Also registers this pass's falsifier flags in the shared list and
regenerates the gallery for the two rebuilt pieces.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Signed-off-by: TMHSDigital <154358121+TMHSDigital@users.noreply.github.com>

Author: TMHSDigital