chore(api): Suppress unknown contract checks by default

[cqjjjzr]

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Summary

The contract lint is too noisy. Don't output unknown entries by default.

Part of #36444 .

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 Type Coverage

Metric	Base	PR	Delta
Type coverage	46.13%	46.13%	+0.00%
Strict coverage	45.62%	45.62%	+0.00%
Typed symbols	25,064	25,068	+4
Untyped symbols	29,599	29,600	+1
Modules	2790	2790	0

[github-actions]

Pyrefly Diff

base → PR

--- /tmp/pyrefly_base.txt	2026-06-03 06:54:50.072067983 +0000
+++ /tmp/pyrefly_pr.txt	2026-06-03 06:54:36.052972422 +0000
@@ -1972,6 +1972,8 @@
     --> tests/unit_tests/commands/test_legacy_model_type_migration.py:1226:44
 ERROR Argument `SimpleNamespace` is not assignable to parameter `orig` with type `BaseException` in function `sqlalchemy.exc.DBAPIError.__init__` [bad-argument-type]
     --> tests/unit_tests/commands/test_legacy_model_type_migration.py:1250:57
+ERROR Could not find name `pytest` [unknown-name]
+   --> tests/unit_tests/commands/test_lint_response_contracts.py:140:77
 ERROR Expected a callable, got `None` [not-callable]
   --> tests/unit_tests/commands/test_reset_encrypt_key_pair.py:18:9
 ERROR Object of class `ModuleType` has no attribute `upgrade` [missing-attribute]