release.sh: consolidate the changelog stops into a single confirmation gate

[epeicher]

What it does

The release now has exactly one interactive stop. The drafting step's edit pause ("Please update readme.txt if needed... press Enter when done") is gone; the flow is: draft/merge silently, show the final = X.Y.Z = block once, ask Is this changelog complete and correct? [y/N].

Rationale

The two stops were historical layers. The edit pause was the only gate in the original script; then the y/N confirmation was added (which re-reads and displays the block anyway), and finally N became a free stop — draft kept, edits kept, re-run lands straight back at the confirmation. At that point pausing inside the run to edit lost its purpose, and every release walked through two prompts to do one job.

Implementation

• Both drafting paths (fresh insert and merge-into-existing-block) now just print a one-line note. The merge path still lists the appended bullets with the semantic-duplicates warning, since that context is invisible once they're merged into the block.
• Editing readme.txt while the prompt waits is supported and documented: the bump commit is git commit -am, so it picks up the file as saved. The gate re-extracts the block after y and re-prints it when it changed between display and confirmation, so the terminal log always shows what actually shipped:

after=$(changelog_block)
if [[ "$after" != "$block" ]]; then
    echo "readme.txt was edited during the prompt. Shipping this '= $new =' block:"
    printf '%s\n' "$after"
fi

• The stop message gains the git checkout readme.txt discard hint that lived in the removed pause. The resume-mode guard (uncommitted readme edits refused after the bump commit was pushed) is unchanged.

Testing instructions

1. bash -n bin/release.sh
2. Piped-input tests against a scratch readme.txt cover the three prompt behaviors: plain y exits 0 with no redisplay; n exits 1 with the "Release stopped" guidance; editing the block while the prompt waits then answering y exits 0 and re-prints the edited block once.
3. ./bin/release.sh <next-version> --dry-run-changelog shows the updated narration (single gate, no pause).