feat(annotate): keep sidebar shortcuts visible with Agent TUI

[leoreisdias]

Context

When the annotate Agent TUI is open and the Content/Files sidebar is closed, the collapsed sidebar shortcuts should still give people a quick way back to those tabs. The previous behavior hid the shortcuts while the Agent TUI was open, which forced people to collapse the terminal first.

What Changed

• Keep the collapsed left-sidebar shortcut rail visible whenever the left sidebar is closed.
• When the Agent TUI is open, position that rail on the Agent TUI divider using the same --agent-terminal-w width variable that drives the resizable terminal.
• Allow SidebarTabs to receive an inline style so placement can be controlled by the parent layout without duplicating the tab UI.
• Preserve the document-side inset while the collapsed rail is visible, so the shortcuts do not cover the document edge.

Screenshot

All closed:

Review Focus

The important behavior to check is the collapsed shortcut rail placement in annotate mode:

• Agent TUI closed: shortcuts remain on the far-left document edge.
• Agent TUI open: shortcuts sit on the Agent TUI border/divider and move with terminal resizing.
• Left sidebar open: the collapsed rail is hidden as before.

Test Plan

• PATH="$PWD/node_modules/.bun/typescript@5.8.3/node_modules/.bin:$PATH" bun run typecheck
• bun run build:review && bun run build:hook
• Plannotator code review completed with no changes requested