ui(motion): Extension Manager TabStrip + CrossFadeStack

[ZhuchkaTriplesix]

Parent

Leftover polish from #482 / epic #477.

Problem

Extension Manager still uses plain SecondaryButton tabs + IndexedStack (hard cut). Workspace homes already use QueryaTabStrip + QueryaCrossFadeStack.

Proposal

• Replace tab buttons with QueryaTabStrip (Installed / Marketplace / Updates; keep Installed count in label)
• Replace IndexedStack with QueryaCrossFadeStack

Acceptance

• Tab changes cross-fade with QueryaMotion tokens
• Tab strip uses sliding indicator (springs when Full)
• Reduced / Off still work; no regression in install/sideload flows

[ZhuchkaTriplesix]

Shipped on dev via #489 (PR targeted dev, auto-close did not fire).