build: generate crates/tui/CHANGELOG.md as a 15-release slice instead of a full manual copy

The /change command embeds this file into every binary via include_str!;
it now carries only recent releases (regenerated by scripts/sync-changelog.sh,
wired into the release checklist). The explicit-version test derives its
fixture versions from the embedded slice instead of hardcoding old ones.

scripts/sync-changelog.sh

@@ -0,0 +1,21 @@
+#!/usr/bin/env sh
+# Regenerate crates/tui/CHANGELOG.md from the workspace root CHANGELOG.md.
+# The /change command embeds this file into the binary via include_str!, so
+# it deliberately keeps only the most recent release sections.
+#
+# Usage: scripts/sync-changelog.sh [sections-to-keep]   (default: 15)
+set -eu
+KEEP="${1:-15}"
+root="$(cd "$(dirname "$0")/.." && pwd)"
+awk -v keep="$KEEP" '
+  /^\[/ && /\]: http/ { exit }
+  /^## \[/ { count++ }
+  count > keep { exit }
+  { print }
+' "$root/CHANGELOG.md" > "$root/crates/tui/CHANGELOG.md"
+printf '%s\n' \
+  '---' \
+  '' \
+  'Older releases: [CHANGELOG.md](https://github.com/Hmbown/CodeWhale/blob/main/CHANGELOG.md) and [docs/CHANGELOG_ARCHIVE.md](https://github.com/Hmbown/CodeWhale/blob/main/docs/CHANGELOG_ARCHIVE.md).' \
+  >> "$root/crates/tui/CHANGELOG.md"
+echo "wrote crates/tui/CHANGELOG.md ($(wc -l < "$root/crates/tui/CHANGELOG.md") lines, $KEEP sections kept)"