Remove sidebar-position controls from plugin row menus

[brsbl]

Human comments

What was wrong

Plugin row menus still exposed sidebar visibility controls even though the unified Customize sidebar surface now owns navigation visibility and order. The dropdown, right-click menu, and compact drawer also did not share one complete set of plugin actions.

What changed

• Gives plugin row dropdowns, context menus, and compact drawers the same focused actions: Open in split when available, View details, then Disable.
• Removes plugin visibility and position controls from row-level menus; Customize sidebar remains their single owner.
• Keeps direct plugin launching unchanged.
• When the active plugin is disabled, returns to Extensions and refreshes installed plugin state.
• Adds focused coverage for menu parity, action order and icons, split availability, details navigation, disable behavior, and the compact drawer.

Screenshots

Both comparisons use the Design Doctrine plugin, the same persisted dev data, and matched viewport and interaction states. Before is current main at 99c0ad718; after is this PR at 9fd2fb7c1.

Desktop before — main	Desktop after — #2916

Compact before — main	Compact after — #2916

How you verified

• Remote CI passed on exact head 9fd2fb7c1: checks, app/server/integration/package tests, Linux and macOS package smoke, and version checks. The unrelated iOS and Node compatibility jobs were skipped by workflow conditions.
• Drove the exact-head branch web app in Chrome for Testing 151.0.7922.71 at 1440×900 and compact touch 390×844.
• Verified dropdown and right-click parity; Open in split creates a second pane; View details navigates correctly; disabling the active plugin returns to Extensions, persists the disabled state, and the QA fixture was restored afterward.
• Verified the compact drawer exposes the same labels, icons, order, and grouping, closes after navigation, and produced no browser console or runtime errors.
• Compared the cumulative diff with main: only PluginNavSidebarItems.tsx and its focused test change. git diff --check passed.
• Per repository policy, CI-equivalent checks were not rerun locally.

BB-Thread-ID: thr_ccffp4w2p2

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