fix: address Bugbot review findings

Fixes three issues identified in code review:

1. High Severity: Prevent script abort when no issues exist
   - Use `|| echo "0"` fallback when grep -c returns non-zero
   - Ensures script continues even with empty issue list

2. Medium Severity: Fetch all issues, not just first page
   - Add `--limit 1000` to gh issue list command
   - Prevents missing older issues beyond default pagination

3. Low Severity: Use exact title matching
   - Change from `grep -qF` to `grep -qFx` for exact match
   - Prevents false positives from substring matches

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: claude

scripts/create_layer3_issues.sh

@@ -26,8 +26,9 @@ fi
 
 # Fetch existing issues to check for duplicates
 echo "Fetching existing Layer 3 issues..."
-EXISTING_ISSUES=$(gh issue list --repo "$REPO" --label "layer-3" --state all --json title --jq '.[].title')
-echo "Found $(echo "$EXISTING_ISSUES" | grep -c .) existing Layer 3 issues"
+EXISTING_ISSUES=$(gh issue list --repo "$REPO" --label "layer-3" --state all --limit 1000 --json title --jq '.[].title')
+ISSUE_COUNT=$(echo "$EXISTING_ISSUES" | grep -c . || echo "0")
+echo "Found $ISSUE_COUNT existing Layer 3 issues"
 echo ""
 
 # Array of statement proofs to create issues for
@@ -54,8 +55,8 @@ create_issue() {
 
     local title="[Layer 3] Prove ${name,,} statement equivalence"
 
-    # Check if issue already exists
-    if echo "$EXISTING_ISSUES" | grep -qF "$title"; then
+    # Check if issue already exists (exact match)
+    if echo "$EXISTING_ISSUES" | grep -qFx "$title"; then
         echo "⊘ Issue already exists: ${title}"
         echo "  Skipping..."
         echo ""