Harden thread reply roleplay E2E

[TheSentinel454]

Why

The desktop smoke suite intermittently times out while opening a seeded thread. On slower runs, the pointer can remain over #general long enough for the channel activity popover to cover the thread summary; the composer can also overlap a summary near the bottom of the timeline. The roleplay test is meant to validate reply anchoring, so transient pointer placement and viewport position should not determine whether it reaches that assertion.

What

• Reproduce the activity-popover overlap in the formerly failing scenario
• Select each seeded thread by its exact head event ID instead of the first summary in the timeline
• Dismiss transient activity UI and center the target summary before clicking it

Risk Assessment

Low — this changes only Playwright test interaction logic. Production code and behavior are unchanged.

Validation

• just ci
• pnpm build:e2e
• Thread reply roleplay smoke spec repeated five times: 20/20 passed

References

• Original failing job: https://github.com/block/buzz/actions/runs/31185005369/job/92895359582
• Reproduced the same pointer-interception timeout locally before applying the fix

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