feat(mobile): improve native reading and composer layout

[wgqqqqq]

Problem

Native Android, HarmonyOS, and iOS chat surfaces still used smaller reading text and several controls below the shared 48-unit mobile target. Multiline drafts and long model labels could be clipped, and iOS typography did not follow Dynamic Type.

Changes

• use shared 16/24 reading typography across native chat and Markdown surfaces
• make composer controls 48 units and let multiline input and model rows grow without clipping
• add Dynamic Type scaling to generated iOS typography and enlarge the attachment-removal hit target
• add narrow-phone, foldable-context, and long-reading preview scenarios across all native galleries
• keep iOS preview state deterministic so scenario drafts are not overwritten

Validation

• pnpm run mobile:ui:check
• node --test src/apps/mobile/design-system/preview/preview-scenarios.smoke.test.mjs
• pnpm run mobile:architecture
• Android: ./gradlew :app:assembleDebug :app:testDebugUnitTest
• HarmonyOS: HAP build and local unit tests
• iOS: simulator build and ./Testing/run-pure-swift-tests.sh
• Visual: HarmonyOS compact narrow-multiline; iPhone 16 Pro standard, XXL, and accessibility-medium Dynamic Type

Remote scenarios

No remote protocol or persisted shape changed. The UI was exercised with deterministic native preview state; Remote Workspace, live Remote Control, Peer Device Mode, and Detached Dispatch were not exercised.