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

docs/workflow-steps.md

@@ -33,6 +33,17 @@ Workflow steps run in one of two phases:
 
 Prompt mode can run with readonly or coding-capable tool access depending on step/template configuration.
 
+## Gate Modes
+
+Workflow steps also have a `gateMode`:
+
+- **`gate`**: failures block merge/completion and follow normal remediation/retry flows.
+- **`advisory`**: failures are recorded as `advisory_failure` and shown as polish feedback, but never block merge.
+
+Defaults:
+- prompt steps → `advisory`
+- script steps → `gate`
+
 ## Built-In Templates (7)
 
 Fusion ships seven templates:
@@ -145,7 +156,7 @@ Not all workflow failures are revision requests:
 
 #### Pre-merge hard failure remediation flow
 
-For pre-merge workflow hard failures, executor behavior is:
+For pre-merge workflow hard failures, executor behavior is (gate-mode steps):
 
 1. Retry the failing check up to `MAX_WORKFLOW_STEP_RETRIES` within the same execution lifecycle
 2. On retry exhaustion, add a steering comment with failure details and inject a `Workflow Step Failure` section into `PROMPT.md`
@@ -158,6 +169,8 @@ Tasks are not parked in `in-review` for this remediable path unless additional t
 
 If a task is found in `in-review` with failed pre-merge workflow results and no active executor, self-healing can auto-revive it (bounded by `maxPostReviewFixes`) by replaying the same remediation send-back flow.
 
+Advisory failures are intentionally excluded from merge blocking and auto-revive.
+
 ## Viewing Results
 
 Workflow status is visible in multiple places: