fix(settings): stop reporting expected pairing channel closes to Sentry

[dschom]

Because

• PairingChannelClient.open() reported every connect failure to Sentry, but a dropped socket is the channel server's normal answer for a channel it will not serve.
• The mobile supplicant hits that on its post-pairing reload — a path the integration already ignores — and on any webview network change.
• Triage already tracks "WebSocket unexpectedly closed" as known client-side noise.

This pull request

• Classifies a closed socket during connect and dispatches CONNECTION_CLOSED (errno 1006) rather than capturing an exception.
• Leaves every other connect failure reporting to Sentry.
• Logs the suppressed close as a console breadcrumb.
• Adds tests for both sides of the split.

Issue that this pull request solves

Closes: FXA-14444

Checklist

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• My commit is GPG signed.
• If applicable, I have modified or added tests which pass locally.
• I have added necessary documentation (if appropriate).
• I have verified that my changes render correctly in RTL (if appropriate).
• I have manually reviewed all AI generated code.

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Other information (Optional)

• 6 of the deleted lines are prettier churn the pre-commit hook applied to pre-existing formatting in the same file.
• create() on the authority side still reports closed sockets; this ticket is scoped to open().
• FXA-14483 (stacked PR) fixes two further defects in the same catch block.