Add setting for update refresh reminders

[AysajanE]

Summary

• add a device-wide setting for the refresh reminder shown after FilterTube updates
• keep the reminder enabled by default for existing and new users
• suppress the reminder across YouTube tabs when the setting is disabled

Checks

• node --test tests/runtime/update-refresh-notification-setting.test.mjs — current base fails for the expected feature absence; patched passes in the clean network-off verifier
• node --check js/background.js
• node --check js/tab-view.js

The repository smoke baseline is unchanged between the exact base and patched trees; no new smoke failure is introduced.

Closes #37

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AI assistance was used. This change was reviewed by Northset, and I accept responsibility for this submission.

Verification

Northset proof-of-pass receipt M-1055
Contributor self-run; not maintainer verification.

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