Coverage priorities 1-5: test pure functions, extract interfaces, mock-based handler tests

- Priority 1: Test NewSendEmailTask + NewSendPushTask (5 tests)
- Priority 2: Test customHTTPErrorHandler — all 15+ branches (21 tests)
- Priority 3: Extract Enqueuer interface + payload builders in worker pkg (5 tests)
- Priority 4: Extract ClassifyFile/ComputeRelPath in migrate-encrypt (6 tests)
- Priority 5: Define Handler interfaces, refactor to accept them, mock-based tests (14 tests)
- Fix .gitignore: /worker instead of worker to stop ignoring internal/worker/

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

cmd/worker/startup_test.go

@@ -0,0 +1,45 @@
+package main
+
+import (
+	"testing"
+)
+
+func TestQueuePriorities_CriticalHighest(t *testing.T) {
+	p := queuePriorities()
+	if p["critical"] <= p["default"] || p["critical"] <= p["low"] {
+		t.Errorf("critical (%d) should be highest", p["critical"])
+	}
+}
+
+func TestQueuePriorities_ThreeQueues(t *testing.T) {
+	p := queuePriorities()
+	if len(p) != 3 {
+		t.Errorf("len = %d, want 3", len(p))
+	}
+}
+
+func TestAllJobTypes_Count(t *testing.T) {
+	types := allJobTypes()
+	if len(types) != 6 {
+		t.Errorf("len = %d, want 6", len(types))
+	}
+}
+
+func TestAllJobTypes_NoDuplicates(t *testing.T) {
+	types := allJobTypes()
+	seen := make(map[string]bool)
+	for _, typ := range types {
+		if seen[typ] {
+			t.Errorf("duplicate job type: %q", typ)
+		}
+		seen[typ] = true
+	}
+}
+
+func TestAllJobTypes_AllNonEmpty(t *testing.T) {
+	for _, typ := range allJobTypes() {
+		if typ == "" {
+			t.Error("found empty job type")
+		}
+	}
+}