Docs/mobile analytics security design

[akinboyewaSamson]

closes #336

Description

This PR introduces two important documentation assets for the PocketPay mobile app:

1. Mobile Security Checklist (docs/mobile-security-checklist.md) – a reviewer‑friendly checklist ensuring that any contribution maintains the high security standards required for handling secret keys, signing flows, logging, screenshots, secure storage, and error handling.
2. Analytics Security Design (docs/analytics-security-design.md) – a design guide that defines safe, privacy‑preserving screen‑level analytics events, covering scope, naming conventions, redaction rules, opt‑out handling, and implementation best‑practices.

Both documents are linked from the project's README.md for easy discoverability.

Motivation

• Security hygiene: Prevent accidental exposure of secret keys or transaction data.
• Analytics privacy: Guard against inadvertent collection of sensitive wallet information while still gathering useful usage insights.
• Review efficiency: Provide clear, structured checklists so reviewers can verify compliance quickly.

Changes Made

• New files:
  • docs/mobile-security-checklist.md
  • docs/analytics-security-design.md
• README updates: Added links under Security and a new Analytics Design section.
• PR documentation files:
  • docs/pr-mobile-security-checklist.md
  • docs/pr-analytics-security-design.md
  • New combined PR doc docs/pr-mobile-analytics-security-design.md (this file).

Testing / Verification

1. Run the app locally and confirm the README links resolve correctly.
2. Execute lint (npm run lint) and test suites (npm test) – no new warnings or failures should appear.
3. Manually review the checklist and analytics design for completeness and correctness.

Review Checklist

• Documentation follows repository style guidelines.
• No new lint warnings introduced.
• Build passes (npm run build / npm start).
• All example events in the analytics design respect redaction rules.
• Links in README are functional.
• Both checklist and analytics design are referenced in PR description.

Related Issues

• None – this is a new documentation addition.

[El-swaggerito]

This PR cannot be merged automatically because it has merge conflicts.

Please update the branch with the latest base branch and resolve the conflicts.

After the conflicts are resolved and checks pass, the automation can review it again.