feat(FN-2383): persist task priority across core storage

- Add task-priority contract, normalization helpers, and exports in @fusion/core types/index
- Store task priority in SQLite and migrate existing databases with default values
- Update task store behavior and sorting tests to preserve and order by persisted priority
- Add migration/regression coverage for archived tasks and refresh storage/task-management docs

packages/core/src/__tests__/store-sort.test.ts

@@ -1,5 +1,6 @@
 import { describe, it, expect, beforeEach, afterEach } from "vitest";
 import { TaskStore } from "../store.js";
+import { sortTasksByPriorityThenAgeAndId } from "../task-priority.js";
 import { rm } from "node:fs/promises";
 import { join } from "node:path";
 import { mkdtempSync } from "node:fs";
@@ -52,4 +53,16 @@ describe("TaskStore.listTasks() sort order", () => {
       expect(nums[i]).toBeGreaterThan(nums[i - 1]);
     }
   });
+
+  it("provides deterministic helper ordering by priority then age then id", () => {
+    const sorted = sortTasksByPriorityThenAgeAndId([
+      { id: "FN-010", createdAt: "2026-01-02T00:00:00Z", priority: "normal" },
+      { id: "FN-001", createdAt: "2026-01-01T00:00:00Z", priority: "high" },
+      { id: "FN-002", createdAt: "2026-01-01T00:00:00Z", priority: "high" },
+      { id: "FN-003", createdAt: "2026-01-01T00:00:00Z" },
+      { id: "FN-004", createdAt: "2026-01-01T00:00:00Z", priority: "urgent" },
+    ]);
+
+    expect(sorted.map((task) => task.id)).toEqual(["FN-004", "FN-001", "FN-002", "FN-003", "FN-010"]);
+  });
 });

packages/core/src/__tests__/task-documents.test.ts

@@ -51,7 +51,7 @@ describe("TaskStore task documents", () => {
 
     expect(tableNames.has("task_documents")).toBe(true);
     expect(tableNames.has("task_document_revisions")).toBe(true);
-    expect(db.getSchemaVersion()).toBe(42);
+    expect(db.getSchemaVersion()).toBe(43);
 
     const index = db
       .prepare(