feat(tasks): add inherited context and resilient LLM execution

Add read-only task context inheritance, ordered task-level LLM failover, live Worker controls, cascading task cleanup, FIFO task concurrency, cancellation diagnostics, UI updates, tests, build script, and changelog.

db/task_source_limit_test.go

@@ -0,0 +1,20 @@
+package db
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestCreateTaskRejectsTooManySourcesBeforeOpeningTransaction(t *testing.T) {
+	sourceIDs := make([]int64, MaxTaskSourceCount+1)
+	for i := range sourceIDs {
+		sourceIDs[i] = int64(i + 1)
+	}
+
+	// No database handle is needed: validation must run before Begin so an
+	// oversized request cannot consume a connection or create partial rows.
+	_, err := (&DB{}).CreateTaskWithOptions("child", "goal", TaskCreateOptions{SourceTaskIDs: sourceIDs})
+	if err == nil || !strings.Contains(err.Error(), "too many source tasks") {
+		t.Fatalf("expected source-count validation error, got %v", err)
+	}
+}