Keep context menus above the Android keyboard

[joepio]

Changes

• Reposition open dropdown and resource context menus on each visual viewport resize or scroll frame, so they follow the Android keyboard.
• Limit menu height to the visible area and keep the action list scrollable above the keyboard.
• Add a browser regression that simulates two keyboard animation steps and checks that the menu and its filter stay visible.

Validation

• Data browser TypeScript: passed.
• Focused lint and formatting: passed (existing lint warnings remain in Dropdown/index.tsx).
• Browser E2E TypeScript: blocked by an unchanged ai-chat-discovery.spec.ts reference to missing Agent.aiChatsFolderSubject on develop.
• Browser test and physical Android keyboard motion: not run locally; the app and server services were unavailable.

[joepio]

Trekmeester: included in batch #1947 (run 36781515104; #1915 had been merged without it). It lands when that run is green; if this PR breaks something there, I take it out and say why here.

[joepio]

Merged into develop through batch #1947 (squash 1f892aa); this head was verified as part of it. Closing.

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