fix(web): relabel merged-PR quick action as "Merged"

[connorch]

What Changed

The quick action button for a checkout with a merged PR now reads "Merged" instead of "View PR". Clicking it still opens the PR as before.

Why

With the merged-state tint added in a prior change, the button already reads as a status chip rather than a call to action. Keeping the "View PR" label alongside that tint was misleading, since the action still opens the PR but the primary signal users need is that it's already merged.

UI Changes

Quick action label changes from "View PR" to "Merged" for checkouts with a merged, unambiguous PR. No layout or interaction changes.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

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