Add a negative-control scenario: successful diagnostics upload

[sepehr-safari]

Good First Issue

Add a scenario diagnostics-upload-success. It is a negative control: a station
that uploads diagnostics successfully must produce no failures.

diagnostics-failure.ts is the only scenario that sends a
DiagnosticsStatusNotification at all, and it sends only a failing status. Nothing
covers the successful path, so a change that widened DIAGNOSTICS_FAILURE to treat
Uploaded or Uploading as a problem would pass the whole suite while reporting
every healthy diagnostics upload as a fault.

What to do

1. Create
   packages/toolkit/src/scenarios/__scenarios__/diagnostics-upload-success.ts
2. Build a synthetic trace of a clean diagnostics upload:
   • BootNotification at 2026-03-01T10:00:00.000Z, and its CallResult with
     interval: 300
   • DiagnosticsStatusNotification with { status: 'Uploading' } at
     10:01:00.000Z, and its CallResult
   • DiagnosticsStatusNotification with { status: 'Uploaded' } at
     10:02:00.000Z, and its CallResult
   • Heartbeat at 10:04:00.000Z, and its CallResult
3. Set expectedFailures: []
4. Add { type: 'no_failures', params: {} } as the assertion
5. Register, update the counts, run the checks and add a patch changeset

Why those statuses

Uploading and Uploaded are the progress and success values a station reports on
a healthy diagnostics upload. Keeping the whole trace inside five minutes of the
boot keeps the heartbeat rules quiet. This trace was run against the detection
engine and reports no failures.

Files to modify

The same seven as Issue A, with the new file named
diagnostics-upload-success.ts.

Guidelines

• Reserves station ID CS-SYNTHETIC-026.
• firmware-update-success.ts is the closest existing negative control to copy,
  since it is the same shape for the firmware equivalent.
• Verify with ocpp-debugkit scenario run diagnostics-upload-success that no
  failures are reported. If a rule fires, fix the trace rather than adding the code
  to expectedFailures. Staying clean is the whole point.
• Everything else as in Issue A.

How to claim

Comment "I'd like to work on this" and it will be assigned to you.

Please hold one open claim at a time. Once the pull request for it is merged, say
which issue you want next and it will be assigned.