fix(release): guard _all_tags read loop against empty elements (Phase 1.5) (#3504)

The Phase 1.5 CHANGELOG completeness gate can report a phantom "missing"
tag with an empty name and bogus commit count under bash 3.2 when the
process substitution `< <(git tag --sort=-v:refname)` leaves an empty
element in the _all_tags array. Skip empty `_t` values inside the read
loop so the array only ever holds real tag names.

Verified by extracting the gate logic and running on bash 3.2:
- Unmodified CHANGELOG.md (all 5 recent tags present) -> "OK" (no phantom)
- Synthesized CHANGELOG with [0.10.2] removed -> correctly flags
  "v0.10.2 (2026-06-15, 5 commits)"

Closes #3501

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

Author: rjwalters

defaults/.claude/commands/loom/release.md

@@ -62,6 +62,7 @@ else
   # Use a portable read loop (avoids `mapfile`, which is bash 4+ only).
   _all_tags=()
   while IFS= read -r _t; do
+    [ -n "$_t" ] || continue   # defensive: skip empty lines from process substitution
     _all_tags+=("$_t")
   done < <(git tag --sort=-v:refname)
   _limit=$RECENT_TAG_COUNT