Land a Pull Requests tab beside the thread as its own branch

[Defmon3]

Seen on: work/stack-6315-refresh-20260829

What it fixes

Pull requests live on their own page. While working in a thread, a user has to leave it to see the project's open pull requests or the one linked to the thread. This piece adds a Pull Requests tab to the thread's right panel, scoped to the active project, showing the list and a selected pull request's details in panel form: no Check out action and no environment picker, which belong to the full page.

Why we need it

It is PR 9 of the series in the Git History series issue (#8) and the first pane piece. It needs nothing from upstream's issues work, so it can land while that is still being split.

How to fix it

Cut a fresh branch from upstream main carrying a project-scoped pull request panel that reuses the list and detail components the pull requests page already uses, in panel context, with the panel's own tests. The PR description states the end state from the series issue. Deferred: the Repository pane and the Issues tab.

[Defmon3]

Technical appendix: Land a Pull Requests tab beside the thread as its own branch

Investigated on branch work/stack-6315-refresh-20260829 at commit 23578f462, the stacked proposal rebased onto the head of upstream PR pingdotgg#6315. Findings marked "verified" were confirmed by an independent review pass on 2026-09-04.

Findings

• apps/web/src/components/pullRequest/PullRequestsPanel.tsx (new, about 630 lines): a project-scoped list and detail host. It passes context="page" unconditionally to PullRequestDetailPanel, and page context is what renders the Check out action and the environment picker, so both appear beside a thread. Verified.
• The same file defines usePanelPullRequestListStats, a copy of the exported usePullRequestListStats in apps/web/src/state/pullRequests.ts. Verified.
• apps/web/src/components/pullRequest/PullRequestListFilters.tsx gains a showProjectScope prop, defaulting to true, that hides the project radio group when the panel is already scoped; the existing routes keep the selector. Verified.
• The base branch has no project-scoped pull request panel; the list lives in the route apps/web/src/routes/_chat.pull-requests.tsx. Upstream main at a6797b3 has the same shape. The proposal's description claims the pull request view is reused; the panel is new code. Verified.
• On the stacked proposal the panel is rendered only inside the Repository pane; there is no standalone right-panel tab for it.

The problem

Observed: pull requests are visible only on the full page, and the only panel version exists on a fork branch with the page-context and duplication defects above.

Once done: a branch from upstream/main adds a Pull Requests tab in the thread's right panel, scoped to the project, using the shared list and detail components in panel context.