Resolve review threads from Summary and Timeline, and apply review suggestions locally

[TonybynMp4]

Before submitting

• I searched existing issues and did not find a duplicate.
• I am describing a concrete problem or use case, not just a vague idea.

Area

apps/web, apps/server

Problem or use case

I go through review feedback in the Pull Request panel a lot, and two things keep pulling me out of it.

1. You can only resolve a review thread from the Code tab. Summary and Timeline already label threads as resolved, but there's no button to change it. So after I reply to a comment in the conversation, I switch to Code and hunt for the same line just to click Resolve.
2. Suggested changes are read-only. A reviewer's ```suggestion block renders as a plain code block. Accepting it means copying the lines by hand, or asking the agent to redo an edit the reviewer already wrote.

#10176 covered part of the first problem, but it was closed for bundling unrelated workflows. I'd keep these as two separate PRs.

Proposed solution

1. Resolve and unresolve from Summary and Timeline. Comments that belong to a review thread get the same resolve control the Code tab already has. GitHub, GitLab and Bitbucket already support the mutation, so this only touches the web app.

2. Apply a suggestion to the local checkout. Suggestion blocks render as a small diff of the commented lines against the suggested ones. An Apply button writes the replacement into the file in the project's checkout. It doesn't commit or push. The change lands in the normal diff, where I can review it, commit it, or hand it to the agent.

Apply refuses, with a reason, when the checkout isn't on the PR's head branch or when the target lines no longer match what the reviewer commented on. I'd rather it fail than patch the wrong lines.

This works the same for every forge because it edits the local file, not the host API. One gap: multi-line suggestions need the thread's start line, and PullRequestReviewThread only carries line today, so the contract needs a startLine.

Out of scope for now:

• Committing through the forge. GitHub's "Commit suggestion" has no public API.
• Batching several suggestions into one change.
• Mobile.

Why this matters

Working through review comments is a loop I run several times a day. Both changes keep it inside the panel, and committing stays my call.