feat(FN-1201): store workflow steps in dedicated SQLite table

- Add schema v16 migration that creates workflow_steps and backfills rows from legacy config.workflowSteps data
- Update legacy file-to-SQLite migration to insert workflow step definitions into workflow_steps while preserving nextWorkflowStepId
- Refactor TaskStore workflow step create/list/get/update/delete paths to read and write workflow_steps instead of config JSON
- Adjust db migration tests and AGENTS.md storage docs to reflect the new workflow_steps table model

packages/core/src/db.test.ts

@@ -96,7 +96,7 @@ describe("Database", () => {
     });
 
     it("seeds schema version", () => {
-      expect(db.getSchemaVersion()).toBe(15);
+      expect(db.getSchemaVersion()).toBe(16);
     });
 
     it("seeds lastModified", () => {
@@ -119,7 +119,7 @@ describe("Database", () => {
 
     it("is idempotent - calling init() twice does not fail", () => {
       expect(() => db.init()).not.toThrow();
-      expect(db.getSchemaVersion()).toBe(15);
+      expect(db.getSchemaVersion()).toBe(16);
     });
 
     it("does not overwrite existing config on re-init", () => {
@@ -726,7 +726,7 @@ describe("schema migrations", () => {
     db.init();
 
     // Verify version bumped to 5 (includes v1→v2, v2→v3, v3→v4, and v4→v5 migrations)
-    expect(db.getSchemaVersion()).toBe(15);
+    expect(db.getSchemaVersion()).toBe(16);
 
     // Verify new columns exist and existing data is intact
     const cols = db.prepare("PRAGMA table_info(tasks)").all() as Array<{ name: string }>;
@@ -751,11 +751,11 @@ describe("schema migrations", () => {
     const db = new Database(kbDir);
     db.init();
 
-    expect(db.getSchemaVersion()).toBe(15);
+    expect(db.getSchemaVersion()).toBe(16);
 
     // Re-init should not fail
     db.init();
-    expect(db.getSchemaVersion()).toBe(15);
+    expect(db.getSchemaVersion()).toBe(16);
 
     db.close();
   });
@@ -771,7 +771,7 @@ describe("schema migrations", () => {
 
     db.init();
 
-    expect(db.getSchemaVersion()).toBe(15);
+    expect(db.getSchemaVersion()).toBe(16);
 
     const tables = db.prepare("SELECT name FROM sqlite_master WHERE type='table' AND name = 'agentRatings'").all() as Array<{ name: string }>;
     expect(tables).toEqual([{ name: "agentRatings" }]);
@@ -874,7 +874,7 @@ describe("schema migrations", () => {
     db.init();
 
     // Verify version bumped to 5
-    expect(db.getSchemaVersion()).toBe(15);
+    expect(db.getSchemaVersion()).toBe(16);
 
     // Verify new columns exist and existing data is intact
     const cols = db.prepare("PRAGMA table_info(tasks)").all() as Array<{ name: string }>;
@@ -1084,7 +1084,7 @@ describe("createDatabase factory", () => {
     const db = createDatabase(kbDir);
     db.init();
 
-    expect(db.getSchemaVersion()).toBe(15);
+    expect(db.getSchemaVersion()).toBe(16);
     expect(db.getLastModified()).toBeGreaterThan(0);
 
     db.close();