[FEATURE] "Delete all my data" in-app control

Description

Per 0007 — Authentication, account recovery, and data-deletion behavior: there's no server-side data to delete (local-only architecture, 0001), but relying on "just uninstall the app" to delete data isn't discoverable or explicit enough. Build an in-app action that immediately wipes the local encrypted database.

Scope: a settings-level "Delete all my data" control and its confirmation/execution flow. Does not include any server-side deletion (none exists) and does not include the backup/export flow — this is destructive, one-way local deletion only.

Acceptance Criteria

• Discoverable "Delete all my data" action exists in-app (e.g., in settings)
• Action requires explicit confirmation before executing (destructive, irreversible — this audience is often tired or distracted, so no accidental one-tap deletion)
• Confirmation copy is plain-language and states clearly that this cannot be undone
• Executing the action wipes the local encrypted database immediately
• After deletion, app returns to a clean/first-run state without crashing or showing stale data
• Meets WCAG-aligned accessibility requirements (screen reader labels, no color-only affordances, adequate touch target size) for both the control and confirmation step
• 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, "Data deletion" section
• Directly satisfies the MVP exit-criteria checklist item on documented deletion behavior (referenced in the ADR)
• Related: onboarding copy about backup responsibility is tracked as a separate ticket, since deletion is unrecoverable and users should understand backup is on them before they ever need this control

QA

• Trigger deletion and confirm local database is actually wiped (not just hidden in UI)
• Confirm confirmation step blocks accidental single-tap deletion
• Test with a screen reader (VoiceOver/TalkBack) that the control and confirmation are announced clearly
• Confirm app doesn't crash or show broken state immediately after deletion