replaceInCurrentMilestone() locates content by finding the last </details>
in the ROADMAP and only operates on text after that boundary. When the
current (in-progress) milestone section is itself wrapped in a <details>
block (the standard /gsd-new-project layout), the phase section's
**Plans:** counter lives INSIDE that block. The replacement target ends up
in the empty space after the block's closing </details>, so the regex never
matches and the plan count stays at 0/N permanently.
Fix: switch the plan count update to use direct .replace() on the full
roadmapContent, consistent with the checkbox and progress table updates
that already use this pattern. The phase-scoped heading regex
(### Phase N: ...) is specific enough to avoid matching archived phases.
Adds two regression tests covering: (1) plan count updates inside a
<details>-wrapped current milestone, and (2) phase 2 plan count is not
corrupted when completing phase 1.
