codeSplitter merge 1: settle list and paragraph one-liners deterministically #933

Design: apps/codesplitter/docs/merge-solutions.md, §3. Measured on the 29 git hunks between main and #893 and #886: today's merge by line id settles 16, and this settles 25.

• L2a diffToOps pairs a changed old line with its most similar new line, not the first one by position. Fixes the worker.ts import, where main's new beamRoutes line took the old import's id.
• L2b In prose and comments, the mergeWords rename guard ignores stopwords and words under 3 letters. Fixes the codeSplitter: tags, made here and traded with upstream (#879) #893 README bullet, which tripped on "a" and "it". Code keeps the full guard.
• L2c A line counts as "doubled" only when it would land twice in the same block, so boilerplate inside two new test bodies doesn't count. Fixes deps.test.ts.
• L3 Inside a stretch both sides reshaped: pair lines by similarity, then merge list items inside each pair ({…}, […], (…), import {…}, ,/; separators, CSS rules, sentences). Add by key, dedupe identical adds, and keep the rename guard per item. Lines only one side has pass through whole, never word-merged.
• Ordering: at a shared spot, main's insert goes first, then the branch's. If the base list was sorted, insert sorted instead.

Fixtures: the hunks in the doc's table, especially the ones where a naive token union breaks (held: f.held.value,, digs rank }, ?? {peers } }) and the multi-line registry fetch in deps.ts:270.