test: stabilize timing-sensitive integration fixtures

[davidahmann]

Problem

Main CI exposed two timing-sensitive test assumptions under parallel runner load:

• concurrent fake gh processes could JSON-parse the shared call log while another process was appending to it
• the OCI preflight test could consume its 100 ms deadline during setup and exercise command timeout instead of image-inspection timeout

Change

• count fake-provider endpoint occurrences from raw log text before appending the current call
• give the OCI preflight fixture one second to enter image inspection, with a separate three-second abort fallback

Production deadlines and runtime behavior are unchanged.

Validation

• GitHub adapter test passed twice consecutively
• OCI deadline test passed three times consecutively
• npm run check
• exact-head local maintainer review: ready, zero findings
• DCO check passed