Export complete activity summaries

[PengfanZ]

What changed

• Export every expense and settlement payment instead of truncating the activity history.
• Add a compact QR code that opens the current Live activity when one exists.
• Redesign the summary with clean grouped surfaces, consistent rounded corners, and no divider-heavy receipt styling.
• Clarify English and Simplified Chinese share copy and documentation.
• Add unit, integration, and browser coverage for complete exports and Live QR rendering.

User impact

Shared summaries now contain the complete activity history. Live summaries also provide a direct QR path back to the editable activity.

Validation

• 503 unit and integration tests passed
• 100% statements, branches, functions, and lines coverage
• 12 core Playwright journeys passed
• 14 AI Playwright journeys passed
• TypeScript, ESLint, and production PWA build passed
• Full-resolution PNG visual QA completed

Remaining risk

Activities with exceptionally many expenses create a correspondingly tall PNG so no records are hidden.