fix(#3854): write normalization preserves tight multi-line lists (#4049)

* test(#3854): write normalization must preserve tight multi-line lists (failing first)

* fix(#3854): no blank before a bullet whose previous line is an indented continuation

_normalizeMd's 'separate a list from a preceding paragraph' rule inserted
a blank before any bullet whose previous line wasn't a bullet — but an
INDENTED CONTINUATION of the previous multi-line item also isn't a
bullet. Every .md write (phase.complete in the report, but any write
through platformWriteSync) therefore converted tight lists to loose
ones: +61 blank lines on the reporter's 1015-line ROADMAP, one before
each bullet following a wrapped item. Tight and loose lists render
differently, so this was a rendering change plus misleading diff noise;
one-shot (idempotent afterwards), which is why integrity checks on
headings/content passed.

The guard is the mirror image of the after-a-bullet rule two lines
below, which already excludes indented next lines. Paragraph→list and
heading→list separations — the rule's purpose — are pinned unchanged by
the new suite.

* fix(#3854): review fold-ins — ceiling tracks next's 281 + this branch's marker (282), header/require nits

The ceiling is not ratcheted but must track the tree: origin/next raised
it to 281 (sibling branch's marker file); this tree adds one more
(shell-command-projection-md-normalize), so 282/282. Also fixes the test
header's stale pre-rename filename and hoists the inline require to the
file's single import.

* chore(#3854): changeset fragment (pr number backfilled after PR creation)

* chore(#3854): backfill changeset PR number (4049)

---------

Co-authored-by: sim <sim@local>

.changeset/calm-tunas-rally.md

@@ -0,0 +1,5 @@
+---
+type: Fixed
+pr: 4049
+---
+writing any markdown file no longer converts tight multi-line lists to loose ones — a blank line was injected before every bullet following a wrapped item (61 blanks on a 1015-line ROADMAP via phase.complete; the defect sat in the write seam every .md write uses), and tight vs loose lists render differently so this was a rendering change plus large misleading diffs, not just whitespace (#3854)