feat(settings): show more account history events

[vbudhram]

Because

• Account History stopped at 20 security events, so users could not see older activity.
• The cap was the .limit(20) in SecurityEvent.findByUid. The page itself never capped anything.

This pull request

• Adds an optional limit argument to SecurityEvent.findByUid and raises the default to 100 (security-event.ts).
• Renders the first 20 events on the Recent account activity page, with a "Show more" button for the rest (PageRecentActivity/index.tsx).
• Caps the list after the HIDDEN_SECURITY_EVENT_NAMES filter, so 20 visible rows show and hidden events stay hidden once expanded.
• Adds the recent-activity-show-more-button string and tests for the cap, the button, and the filter.

One side effect worth knowing: GET /account returns this same list, so it now returns up to 100 entries. The page seeds its first render from that field, so both sources need the same limit.

Issue that this pull request solves

Closes: https://mozilla-hub.atlassian.net/browse/FXA-14318

Checklist

• 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.

Other information

How to test: open Settings, then "Recent account activity". An account with more than 20 events shows 20 rows and a "Show more" button that reveals the rest.

[vpomerleau]

I thought the ticket was intended for the admin panel "Account history", but maybe I misunderstood?

Nice improvement to settings though, this also mitigates something I noticed on another ticket, where the rendered list could come up shorter than 20 when some events are hidden. Filtering after fetching 100 means its pretty guaranteed that we'll have 20+ visible.

[vpomerleau]

Should we also have a reverse button to collapse the list once it's expanded? And/or only show an additional 20 with each "show more" click?