Fix PUT /page/:pageid Column Generation Behavior

[thehabes]

Closes #502.

PUT /page/:pageId was creating one new column per new line item. This was observed when the "Detect Lines" prompts submit all lines in a single PUT, which produced N single-line columns whose order had no relationship to reading order — breaking line-by-line navigation.

Change

Removed the auto-column-create branch in the updatedItemsList loop and unwrapped the surrounding else so the split-into-existing-column logic runs unconditionally.

Preserved behavior

• Existing-column line-id remapping when RERUM versions a changed line.
• Splitting a RERUM-tracked line: numeric date-id children are appended to the parent's column.
• Line deletion: dropped lines leave their column; empty columns are deleted.
• Explicit column creation via POST /page/:pageId/column is unchanged.

Side effect

pageColumnsUpdate.find(...) is now pageColumnsUpdate?.find(...). The new block runs for every updatedItemsList entry, so the variable can legitimately be null (column-less page). Closes a latent null-deref on column-less pages whose lines get RERUM-versioned by a PUT.

Manual testing

#	Scenario	Starting state	Request	Result
1	Bulk-create on a page with one column	1 line, 1 column (A)	echo existing line + 2 brand-new lines	✅ 3 items, Column A unchanged, no new columns
2	Single-column split	continued from 1	parent line (body change) + 2 numeric date-id children + 2 preserved lines	✅ 5 items; Column A tracked new parent URI and gained both split children
3	Line deletion from a column	continued from 2	4 items; one column-tracked child omitted	✅ Column dropped the omitted child; tracked new URIs for the rest
4	No-op PUT (re-versioning guard)	reset: 1 line, 1 column	same id + same target, no body	✅ URI unchanged — hasAnnotationChanges correctly skipped re-versioning
5	Multi-column split with brand-new line in same PUT	reset: 2 lines, 2 columns (A, B)	A (body edit) + numeric child for A; B (body edit) + numeric child for B; 1 brand-new line	✅ Both columns tracked their new parent URI and gained their own child only; brand-new line created no third column
6	Bulk-create on a column-less page	different page: 1 line, 0 columns	echo existing line + 5 brand-new lines	✅ 6 items in submission order; columns still null; existing URI preserved (target unchanged); the new pageColumnsUpdate?.find(...) null-safety branch exercised

[cubap]

worked as tested