test(integration): repair pre-existing integration test failures (fully green CI)

[hellodk]

Summary

Repairs the integration-test gate, which has been red on master independent of any single PR. None of these failures were caused by the agent epic or the dependency bump — they are accumulated test drift across several subsystems.

File	Root cause	Fix
test_process_stats_read_609	local viewer_token fixture used the old create_access_token({...}) dict signature; seeded nodes missing first_seen_at	drop the shadowing fixture (use conftest's), set first_seen_at
test_node_action_execution_614	referenced a non-existent db fixture; nodes missing node_token_hash/first_seen_at; handlers now slowapi-decorated (need Request); approve now async (apply_async → executing)	add db→db_session alias, set required cols, pass a Request, update to the async dispatch contract
test_process_stats_ingest	registered_node_client fixture never defined	add the fixture (Node + X-Node-Token client)
test_salt_keys_api	tests mocked a removed filesystem _dirs helper	rewrite to mock the salt-api wheel client (key.list_all/accept/reject/delete, degraded/502 paths)
test_test_email_api	route reads SMTP settings via an un-overridden sync session → platform_settings missing in test DB	mock send_test_email to exercise the 400 path

Test plan

• All 36 tests across the 5 touched files pass locally against a disposable Postgres
• ruff check / ruff format clean
• CI integration gate green on PR

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[github-actions]

Coverage Report

✅ 85.1% on fleet_platform/services/ (gate: 80%)

Gate passed