docrot v1.6.0 — Scanner v8: two more phantom classes closed

v1.6.0 / Scanner v8: fence indent 0-7 + list-item-local pairing — two more phantom classes closed

Found during manual classification of the v7 rescan (before-publishing
rule, again): BOTH defects were phantoms inside the freshly produced v7
datasets. Nothing was published from v7.

1. airbnb/javascript 'react/hello.jpg' (wave 2): the reference lives in a
   4-space-indented ```jsx fence inside a list item; GitHub renders it as
   code (verified in rendered HTML) but the fence regex only stripped
   indent 0-3. CommonMark allows up to 3 spaces BEFORE the list marker,
   so fences inside items legitimately sit deeper -> strip 0-7.

2. jujumilk3 '' (wave 3): the code span's opener sits in one
   list item, content+closer after a blank line in the next; an odd
   backtick run in the first item shifted positional pairing and left the
   span content live. Pairing now splits at list-item starts
   (_pair_backtick_runs), still paragraph-local within items.

Schema version 7 -> 8. Suite 87 -> 89 (both real-file shapes as
regressions; the jujumilk3 fixture topology verified against GitHub
HTML: that item renders ).

Also ships tools/synthesize_v8.py: 300-repo v5->v6->v7->v8 synthesis
with hard expectation gates (E1a airbnb 0, E1b jujumilk3 2, E1c skills
0, E2 webpack 327) committed BEFORE any v8 result exists; exit 2 on
incomplete inputs, exit 3 blocks publication on red.