feat(code): use remote files for cloud review panel

[adboio]

Problem

the cloud diff review panel constructs a diff from the agent output. this is fine, but makes it harder to ensure the panel is up-to-date with remote branch or PR, which means it'd be hard to do cooler stuff with PR comments/CI/etc in the future

Changes

swaps out the cloud review panel to always use a diff from the PR or the remote branch, never constructed from agent changes

• agent changes are still visible in realtime in the chat thread
• changed files list in the sidebar still uses agent output for lisitng the files

How did you test this?

manually

[adboio]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• fix(code): truncate text properly in tool call output #1498
• feat(code): remove right sidebar #1497
• feat(code): tree view for changed files list #1494
• feat(code): use remote files for cloud review panel #1491 👈 (View in Graphite)
• feat(code): remove cloud status bar, add pr view button #1476
• main

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