fix: use portable grep -E and restore fetch in collision check

- grep -Eq instead of grep -q with non-POSIX \+ (portability fix)
- Restore git fetch before collision check in both scripts:
  correctness over performance — without fetch, remote-only branches
  are invisible and collisions go undetected

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: fsilvaortiz

scripts/bash/create-new-feature.sh

@@ -251,7 +251,7 @@ if [ "$USE_TIMESTAMP" = true ]; then
 else
     # Validate --number input when provided
     if [ -n "$BRANCH_NUMBER" ]; then
-        if ! echo "$BRANCH_NUMBER" | grep -q '^[0-9]\+$' || [ "$((10#$BRANCH_NUMBER))" -lt 1 ]; then
+        if ! echo "$BRANCH_NUMBER" | grep -Eq '^[0-9]+$' || [ "$((10#$BRANCH_NUMBER))" -lt 1 ]; then
             >&2 echo "Error: --number requires a positive integer, got '$BRANCH_NUMBER'"
             exit 1
         fi
@@ -287,8 +287,9 @@ else
             done
         fi
 
-        # Check git branches for collision
+        # Check git branches for collision (fetch to catch remote-only branches)
         if [ "$NUMBER_IN_USE" = false ] && [ "$HAS_GIT" = true ]; then
+            git fetch --all --prune 2>/dev/null || true
             branches=$(git branch -a 2>/dev/null || echo "")
             if [ -n "$branches" ]; then
                 while IFS= read -r branch; do

scripts/powershell/create-new-feature.ps1

@@ -233,9 +233,10 @@ if ($Timestamp) {
             }
         }
 
-        # Check git branches for collision
+        # Check git branches for collision (fetch to catch remote-only branches)
         if (-not $numberInUse -and $hasGit) {
             try {
+                git fetch --all --prune 2>$null | Out-Null
                 $branches = git branch -a 2>$null
                 if ($LASTEXITCODE -eq 0 -and $branches) {
                     foreach ($branch in $branches) {

tests/test_timestamp_branches.py

@@ -466,7 +466,7 @@ def test_powershell_has_number_collision_validation(self):
         # Must check specs directory for collision
         assert "manualNumPadded" in contents
         # Must check git branches for collision
-        assert "git branch -a" in contents
+        assert "git fetch --all --prune" in contents
         # Must warn and auto-detect on conflict
         assert "conflicts with existing branch/spec" in contents
         # Must skip validation when -AllowExistingBranch is set; allow flexible whitespace