feat(code): remove right sidebar

[adboio]

Problem

🌶️ take: changed files & file tree do not deserve the real estate they currently have

• changed files are useful as a quick reference at what the agent has done, but we can do it better
• (i think) the file tree is somewhat useless
• review panel would be nice to see in a split view, as a better realtime log of what the agent is doing
• review panel being a "tab" is kinda wonky, it's not really a tab in the way one usually thinks about tabs
• i want more/better surface area to eventually show PR details - comments, CI, "review" skills/workflows, tours, etc

Changes

tl;dr - right sidebar is gone, review panel can be toggled on as a sidebar and expanded to full width

• removes the static right sidebar entirely
• removes the file tree... for now... not deleted, but need to figure out where it belongs (or if it belongs)
• adds a new "diff" toggle in the top-right that toggles on/off a review panel sidebar
• review panel can be expanded to full-screen, and shows the changed files list (:evergreen_tree:) there
• a few various UX things here and there to support this
  • "open in..." button is now just an icon

default view - no right sidebar	review toggled on (diff button in top right)	review mode expanded

How did you test this?

manually

[adboio]

• feat(code): show PR comments in review panel #1536
• refactor sending prompt to agent from UI #1539
• chore: add relative time utils #1535
• feat(code): add PR status and actions to cloud tasks #1525
• fix(code): truncate text properly in tool call output #1498
• feat(code): remove right sidebar #1497 👈 (View in Graphite)
• feat(code): tree view for changed files list #1494
• feat(code): use remote files for cloud review panel #1491
• feat(code): remove cloud status bar, add pr view button #1476
• main

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