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/db.ts

@@ -86,7 +86,7 @@ export function probeFts5(db: DatabaseSync): boolean {
 
 // ── Schema Definition ────────────────────────────────────────────────
 
-const SCHEMA_VERSION = 42;
+const SCHEMA_VERSION = 43;
 
 function normalizeTaskComments(
   steeringComments: SteeringComment[] | undefined,
@@ -152,6 +152,7 @@ CREATE TABLE IF NOT EXISTS tasks (
   id TEXT PRIMARY KEY,
   title TEXT,
   description TEXT NOT NULL,
+  priority TEXT DEFAULT 'normal',
   "column" TEXT NOT NULL,
   status TEXT,
   size TEXT,
@@ -1700,6 +1701,19 @@ export class Database {
       });
     }
 
+    // Task priority contract (FN-2383)
+    // Adds priority column and normalizes legacy/missing values to 'normal'.
+    if (version < 43) {
+      this.applyMigration(43, () => {
+        this.addColumnIfMissing("tasks", "priority", "TEXT DEFAULT 'normal'");
+        this.db.exec(`
+          UPDATE tasks
+          SET priority = 'normal'
+          WHERE priority IS NULL OR priority = '' OR priority NOT IN ('low', 'normal', 'high', 'urgent')
+        `);
+      });
+    }
+
   }
 
   /**