Split Plugins and Skills into separate workspaces

[brsbl]

Human comments

What was wrong

• Plugins and Skills shared an Extensions workspace, while installed plugins lived in Settings.

What changed

• Give Plugins and Skills separate sidebars: Browse plugins / Installed plugins, and Browse skills / My skills.
• Use /plugins and /skills, with legacy redirects. Preserve plugin settings, the palette command, SDK identifiers, sidebar preferences, and Browse state/focus.
• Match sidebar and + menu icons: Plug02 for Plugins, unchanged Zap for Skills, Repeat for Automations.
• Render installed plugin details once and skip unused catalog requests.

How you verified

• CI green on 1607741d5: tests, typecheck, lint, and Linux/macOS packaging on Node 22. Regression tests cover redirects, trailing slashes, preferences, palette navigation, Settings memory, Browse focus, single detail mounting, and deferred catalog requests. All 19 redirect cases use the real app router.
• Chrome for Testing 153.0.8010.36 at 1607741d5, 1440×900: cold Installed plugins catalog requests fell from 1 to 0; installed detail trees from 2 to 1, with metadata intact. Manual Browse-focus recheck was blocked by browser-input automation; its regression test passed.
• Chrome for Testing 153.0.8010.36: pre-rebase QA at 7b0191d7c covered all four pages, active states, reload, Back to app, drawers, and Guide icons.
• Desktop comparison: 04f4e6a21 → 7b0191d7c, 1440×900, DPR 1. Phone captures: 6f63ed5a3, 390×844, mobile/touch emulation, DPR 3. Light theme; all mobile sidebars shown open.

View	Before — 1440×900	After — web/desktop 1440×900	After — phone emulation 390×844
Main navigation
Browse plugins
My skills

BB-Thread-ID: thr_czdxmmyenv

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