feat(FN-4468): add workflow step gateMode advisory gating

Adds an "advisory" `gateMode` option for workflow steps: steps in advisory mode log findings but no longer block merge completion, while steps that must block can still be configured as blocking. The change covers the workflow step types and schema, executor gating logic, dashboard UI in WorkflowSte

Fusion-Task-Id: FN-4468

packages/core/src/db-migrate.ts

@@ -160,6 +160,7 @@ async function migrateConfig(fusionDir: string, db: Database): Promise<void> {
       mode,
       phase,
       prompt,
+      gateMode,
       toolMode,
       scriptName,
       enabled,
@@ -168,7 +169,7 @@ async function migrateConfig(fusionDir: string, db: Database): Promise<void> {
       modelId,
       createdAt,
       updatedAt
-    ) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+    ) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
   `);
 
   for (const step of workflowSteps) {
@@ -189,6 +190,7 @@ async function migrateConfig(fusionDir: string, db: Database): Promise<void> {
       mode,
       phase,
       mode === "prompt" ? step.prompt || "" : "",
+      step.gateMode ?? (mode === "script" ? "gate" : "advisory"),
       mode === "prompt" ? step.toolMode ?? null : null,
       mode === "script" ? step.scriptName ?? null : null,
       step.enabled === false ? 0 : 1,