fix: Update CI workflow and close stale issues

**CI Improvements:**
- Fix Go version: 1.25 → 1.23 (matches go.mod)
- Add coverage threshold check (fail <50%, warn <55%)
- Coverage check runs after tests, before codecov upload

**Issue Cleanup:**
- Close bd-1: Stale test issue from early development
- Close bd-2: Auto-export verified working
- Close bd-9: Collision resolution complete (all subtasks done)
- Close bd-69: Coverage threshold implemented

**New Issues:**
- bd-69: CI coverage threshold (completed this session)
- bd-70: Test coverage improvements for auto-flush/import

Addresses review findings. System is now clean and ready for plugin testing (bd-64).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

.github/workflows/ci.yml

@@ -16,7 +16,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v5
         with:
-          go-version: '1.25'
+          go-version: '1.23'
 
       - name: Build
         run: go build -v ./cmd/bd
@@ -24,6 +24,19 @@ jobs:
       - name: Test
         run: go test -v -race -coverprofile=coverage.out ./...
 
+      - name: Check coverage threshold
+        run: |
+          COVERAGE=$(go tool cover -func=coverage.out | grep total | awk '{print $3}' | sed 's/%//')
+          echo "Coverage: $COVERAGE%"
+          if (( $(echo "$COVERAGE < 50" | bc -l) )); then
+            echo "❌ Coverage is below 50% threshold"
+            exit 1
+          elif (( $(echo "$COVERAGE < 55" | bc -l) )); then
+            echo "⚠️  Coverage is below 55% (warning threshold)"
+          else
+            echo "✅ Coverage meets threshold"
+          fi
+
       - name: Upload coverage
         uses: codecov/codecov-action@v4
         if: success()
@@ -40,7 +53,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v5
         with:
-          go-version: '1.25'
+          go-version: '1.23'
 
       - name: golangci-lint
         uses: golangci/golangci-lint-action@v6