[FEATURE] Onboarding copy: backup is the user's responsibility

[Jberma23]

Description

Per 0007 — Authentication, account recovery, and data-deletion behavior: since the journal is local-only with no server backup, losing the device without ever having made an encrypted backup (0003) means the journal is unrecoverable. This is an accepted risk, not something to engineer around — but it needs to be said plainly during onboarding so users aren't surprised later.

Scope: add one honest, plain-language line to onboarding copy communicating that the journal stays on-device and backup (if wanted) is the user's responsibility. Does not include building the backup/restore feature itself (0003, Risk 2 — separate, contingent ticket).

Acceptance Criteria

• Onboarding includes a plain-language line communicating: "this stays on your phone — back it up if you want a copy that survives losing the phone" (or equivalent wording, reviewed for tone)
• Copy avoids alarming or technical language, consistent with the app's compassion-over-complexity principle
• Placement doesn't add friction to onboarding (one line, not a new screen/step requiring extra taps)
• Meets WCAG-aligned accessibility requirements (readable by screen reader, sufficient contrast/no color-only meaning)
• The feature/s being implemented are covered by unit tests - If not, create tests for them on this ticket

Additional Info and Resources

• Source: 0007-authentication-recovery-deletion.md, "Account recovery" section and Consequences
• Related: this line should stay accurate to whatever backup capability actually exists — currently none is built; revisit wording if/when 0003 Risk 2 (device-transfer backup/restore) ships
• Product owner (Roberta Talmage) should review final wording for tone/plain-language fit

QA

• Confirm the line appears during onboarding without requiring an extra step
• Have a non-technical reviewer confirm the copy reads as reassuring/plain, not alarming
• Test with a screen reader that the line is announced correctly