fix: overhaul default model settings across workflow apps and tools

[shenkaibo]

Summary

One combined fix set covering default-model configuration for workflow applications and tools — from persistence/execution correctness through the panel UI and per-category parameter dialog.

This PR squashes 8 prior commits into one and includes fixes for the following bugs/issues:

Data loss — copy operations

• Copying a workflow application dropped its default model configuration: the WorkflowRequest serializer neither declared nor mapped default_model_setting, so DRF silently discarded it and the copy had empty dropdowns in the default-model settings panel.
• Copying a workflow tool lost its default model settings: tool creation (ToolSerializer.Create.insert) built the ToolWorkflow row with only work_flow. default_model_setting is now passed through so the copy keeps it.

Missing-default execution

• A node in "default" model mode kept running the last configured model after that default was cleared: base step-node implementations left stale node_data.model_id. They now always resolve model_id from default_model_setting in "default" mode (None when unconfigured), so debug fails fast with the existing empty-model error, matching publish-time validation — across all affected step nodes.

Panel behavior (default-model-setting)

• Staged edits on close: closing without save let nodes pick up non-persisted config and debug still succeeded. Edits are now staged locally and only committed on save, with an unsaved-changes confirm (save / discard / cancel) on close; the panel mounts via v-if so its click-outside listener is not live while collapsed.
• Publish validation highlight: when a missing default model blocks publish validation, the offending problem node was not highlighted on the canvas — it is now located and highlighted.
• Long-term memory field position: the AI model config field position did not match the prototype; repositioned to match.
• Save-button gating: save button stayed enabled with nothing changed; now disabled when there are no unstaged modifications.
• Readonly support: read-only users could not see/open the default-model settings at all (button gated on edit-level permission). Re-gated on the read-level (debug/read) condition and the panel is view-only for them (model select, param button, apply-to-all, save disabled; hasChanges always false).
• Reranker param button: the parameter-settings button was enabled for RERANKER, which has no parameter form; now disabled for that category.

Param dialog flash (AIModeParamSettingDialog)

• Opening a model's parameter config flashed the previous category's content (~1s) before showing the correct one: the dialog reused the prior model_form_field on a destroy-on-close remount, so DynamicsForm rendered the last category's params until the async getModelParamsForm resolved. Fields are now cleared before the dialog shows, and the body is wrapped in a v-loading mask covering the async window.

Files

• Backend: application workflow step-node impls (12), application.py, tool.py, locales.
• Frontend: default-model-setting/index.vue, AIModeParamSettingDialog.vue, workflow views, validate.ts, nodes.