feat(dify-builder): name apps from their prompt, and turn gate actions into card options

Two App Builder spec changes that share the Builder session contract.

Naming (spec N1-N3): an app created from the homepage prompt is no longer named
by the user. core/dify_builder/naming.py cuts the prompt's opening clause at
create time -- instant and infallible, since it runs inside POST /apps -- and
CreateAppPayload.name becomes optional alongside a new prompt field. The Builder
then refines that name once during goal analysis, where a model and the detected
reply language are already in hand, so the judgement calls that are
English-shaped in pure Python (dropping an imperative lead-in, spotting a
contentless prompt) work in any language. Plan approval freezes the name.

Card options: SessionView gains a Decision carrying the gate's choice as options
inside the card plus a fixed confirm/cancel pair, replacing a button row whose
shape changed at every state. Option ids are the old action ids untouched, so
resolve_action_kind and the per-state legality check are unchanged, and
SessionView.actions keeps being populated -- the deployed web client goes on
working until it reads decision instead.

The regenerated console OpenAPI doc also picks up ErrorCard.diagnostics, missed
when cc9ca8b1dd landed.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

api/controllers/console/dify_builder_fields.py

@@ -16,6 +16,7 @@ from core.dify_builder.contract import (
     ChangeSetCard,
     CheckpointCard,
     CheckpointRef,
+    Decision,
     DecisionItem,
     ErrorCard,
     ErrorEventData,
@@ -52,6 +53,10 @@ class DifyBuilderCreateBuildSessionPayload(DifyBuilderPayload):
     app_id: NonEmptyString
     scenario: Literal["build"]
     goal_text: NonEmptyString
+    # True when the app was created from this same prompt and still carries the
+    # name cut from it, so Builder may rewrite it once it understands the goal.
+    # False is create-from-blank: the user named the app, Builder inherits it.
+    derive_app_name: bool = False
     model_config_data: SessionModel | None = Field(default=None, alias="model_config")
 
 
@@ -252,6 +257,7 @@ class DifyBuilderSessionViewResponse(ResponseModel):
     entry_mode: EntryMode = EntryMode.FIX
     phase: Phase = Phase.UNDERSTAND
     actions: list[Action] = Field(default_factory=list)
+    decision: Decision | None = None
     active_interaction: DifyBuilderActiveInteractionResponse | None = None
     checkpoint: CheckpointRef | None = None
     recovery: RecoveryRef | None = None