Restore Installed plugins in Settings alongside Plugins

[SawyerHood]

Human comments

What was wrong

Splitting Plugins and Skills into separate workspaces removed installed-plugin management from Settings and redirected its existing routes into Plugins.

What changed

Restore Settings → Installed plugins while retaining Plugins → Installed plugins. Both locations manage the same installed plugins, and opening a list row keeps its detail page in the originating section. Restore Settings navigation memory and route the command palette and general installed-plugin links to Settings. Keep individual plugin configuration pages and legacy workspace routes working. Update the agent guide and navigation documentation.

How you verified

• Turbo app typecheck and lint passed (lint has existing warnings, no errors).
• Focused Turbo app tests passed: 86 tests covering both installed-plugin collections/details, Settings and Plugins sidebars, canonical routes, and compatibility navigation. Earlier focused checks also covered command palette, Settings route memory, notification links, and update/configuration links.
• Browser verification in an isolated source dev app: clicked Installed plugins and BB guide from both Settings and Plugins, checked destination URLs and a single detail heading, and confirmed Settings stays selected for its detail page.
• EAP codename scanner passed for the working tree, tracked HEAD, added lines, and commit messages in the push range.
• SlopCop skipped at the user's request.

AGENT GENERATED