feat: app list for onboard

[hjlarry]

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Summary

Screenshots

Before	After
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Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran make lint && make type-check (backend) and cd web && pnpm exec vp staged (frontend) to appease the lint gods

[github-actions]

Pyrefly Diff

base → PR

--- /tmp/pyrefly_base.txt	2026-05-18 08:46:31.754584552 +0000
+++ /tmp/pyrefly_pr.txt	2026-05-18 08:46:24.591520946 +0000
@@ -558,6 +558,8 @@
   --> services/document_indexing_proxy/duplicate_document_indexing_task_proxy.py:15:5
 ERROR `handled_tenant_count` was assigned in the current scope before the nonlocal declaration [unknown-name]
   --> services/plugin/plugin_migration.py:92:34
+ERROR Returned type `Sequence[RecommendedApp]` is not assignable to declared return type `list[RecommendedApp]` [bad-return]
+  --> services/recommend_app/database/database_retrieval.py:94:16
 ERROR `dict[str, Any]` is not assignable to attribute `credentials` with type `Never` [bad-assignment]
    --> services/trigger/trigger_provider_service.py:487:40
 ERROR `int` is not assignable to attribute `credential_expires_at` with type `Never` [bad-assignment]

[github-actions]

Pyrefly Type Coverage

Metric	Base	PR	Delta
Type coverage	0.00%	43.71%	+43.71%
Strict coverage	0.00%	43.24%	+43.24%
Typed symbols	0	22,160	+22,160
Untyped symbols	0	28,849	+28,849
Modules	0	2558	+2,558