fix(api): test connections with current OAuth credentials

[frahlg]

Refs #1502. Depends on #1508. Includes the commits from #1517.

Test connection now uses the configured driver's current OAuth token instead of the original YAML token. It shares secrets only for the same saved name and Lua file. An explicit replacement token stays separate from the working account.

The probe uses the credential owner from #1508 for reads and durable writes. After a changed shared token has been saved and the probe removed, it restarts the configured live driver so that driver loads the new token. An unchanged token does not restart the driver. The restart target comes from the matched live driver, addressing the review on #1517.

Regression tests use a credential owner that differs from the display name and check the token actually read by the restarted Lua driver. Both changed-token and unchanged-token tests failed before the owner integration and now pass.

Validation: targeted API tests, make verify, and race-detector tests for config, state and driver probes pass on the combined branch. The earlier rotation/restart fix also has the hardware evidence recorded in #1517; the combined owner integration has not yet run on that customer's box.

[segran2]

Hardware validation / follow-up from a real FTW site (v0.139.2-beta.6 candidate):

The shared-refresh-token race described in this PR was reproduced on beta.5: after a successful MyUplink Test connection, the probe rotated/persisted the shared refresh token while the live myuplink driver kept the older token in Lua memory. On the next refresh the live driver entered a repeated HTTP 400 invalid_grant loop; restarting FTW recovered immediately by re-reading the persisted token.

A follow-up fix was tested that restarts the live driver after a probe successfully changes a shared persisted secret (probe removal first, then RestartByName for the secret owner). Hardware result:

• Test probe became ready (read-only).
• Probe was removed.
• Live myuplink was immediately removed/restarted.
• Live MyUplink became ready (read-only) again ~320 ms later.
• Persisted refresh-token SHA3-256 changed, confirming an actual rotation.
• Repeated Test connection runs at 18:39, 19:37 and 19:52 all followed the same successful restart/re-ready sequence.
• No invalid_grant occurred afterward, including well beyond the previous ~1 h failure window.

The candidate change was also covered by targeted tests for restart-on-rotation and no-restart-when-unchanged, go test ./internal/api -count=1, and the local CI script.

This provides physical-hardware confirmation that restarting the live driver after probe rotation resolves the stale in-memory refresh-token failure mode.

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