fix(#2853): roadmap.update-plan-progress preserves hand-written annotations (#2916)

* test(#2853): add failing-first regression for plan-progress annotation preservation

The count-bump regex's trailing [^\n]+ swallowed the whole Plans line and
the replacement wrote back only the regenerated count, deleting any
hand-written annotation after it. 8-row matrix covers bold/plain forms,
bare template form, executed path, CRLF, and idempotency.

* fix(#2853): preserve hand-written annotations in roadmap plan-progress bump

The count-bump regex's trailing [^\n]+ swallowed the entire Plans line and
the replacement wrote back only the regenerated count, deleting any
hand-written prose after the count (e.g. a gap-closure annotation).

The verb owns the count token only. Capture the existing count token ($2)
and the trailing line text ($3), and rebuild the line as
<label><new count><surviving text>. Trailing text is preserved ONLY when a
real count token preceded it, so the fresh-template bracketed placeholder
(`[Number of plans…]`) is still replaced cleanly rather than glued after
the count (pre-#2853 behaviour on the template path preserved). CRLF \r is
preserved via [^\r\n].

Widens replaceInCurrentMilestone to accept a replacement callback (needed to
branch on whether the count group matched). The bare Plans: checklist header
is still skipped — the lazy match lands on the summary line first and a
count-less bare header yields no count to anchor preservation to.

* changeset(#2853): backfill PR number 2916

---------

Co-authored-by: Test <test@example.com>
Co-authored-by: sim <sim@local>

src/roadmap-parser.cts

@@ -194,15 +194,25 @@ function extractCurrentMilestone(content: string, cwd?: string): string {
 /**
  * Replace a pattern only in the current milestone section of ROADMAP.md.
  */
-function replaceInCurrentMilestone(content: string, pattern: RegExp, replacement: string): string {
+type RoadmapReplacer = (match: string, ...captures: string[]) => string;
+
+function replaceInCurrentMilestone(
+  content: string,
+  pattern: RegExp,
+  replacement: string | RoadmapReplacer,
+): string {
+  const apply = (src: string): string =>
+    typeof replacement === 'function'
+      ? src.replace(pattern, replacement)
+      : src.replace(pattern, replacement);
   const lastDetailsClose = content.lastIndexOf('</details>');
   if (lastDetailsClose === -1) {
-    return content.replace(pattern, replacement);
+    return apply(content);
   }
   const offset = lastDetailsClose + '</details>'.length;
   const before = content.slice(0, offset);
   const after = content.slice(offset);
-  return before + after.replace(pattern, replacement);
+  return before + apply(after);
 }
 
 /**