cloud-assert A7: read PO: marker from status JSON (DOCFIX-087) ...

Identifier consumed: DOCFIX-087. juju 3.6 --format=line omits workload
messages, so A7's line-format grep false-FAILed a healthy policy override
(found live at ops-update-20260705 pre-flight; window HELD on operator
Option B ruling until this true-PASS fix landed). A7 now greps the
application-status message + all unit workload messages from --format=json;
fail-closed on parse failure. Harness: truthful JSON fixtures replace the
line-format fiction; new T10 regression case; 10/10, gauntlet 31/31.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FCGjrRXtbPRu5qEThw3CDz

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