feat(ios): add composer attachments and push notifications

[Tutitoos]

Plan reference

Post-1.0 — iPhone and iPad: compose and notifications.

Objective

Add native composition, synchronized drafts, replies, forwarding, attachment transfer, idempotent send, and privacy-safe APNs notifications.

Scope

• Implement recipients, subject, rich or supported formatted body with plain text, draft revisions, autosave, conflict recovery, file and photo attachment selection, upload and download progress, send status, APNs registration, device-token rotation, notification privacy, and deep links.

Tasks

• Define Swift 6 models, actors, storage, API, and UI boundaries for this scope.
• Implement the smallest complete native capability.
• Add XCTest, Swift Concurrency, migration, UI, accessibility, and device tests where applicable.
• Update generated clients, translations, privacy declarations, and distribution documentation.

Acceptance criteria

• Drafts survive termination and reconcile without overwriting newer server revisions.

• Send retries cannot duplicate a confirmed message.

• Attachment limits, cancellation, authorization, and recovery match the CDN contract.

• Notification previews default to privacy-safe content and deep links reauthorize before opening mail.

• Account isolation, data protection, accessibility, EN default, and ES completeness match the web and macOS contracts.

• Tokens, credentials, message content, recipients, and personal data never enter logs, crash reports, screenshots, fixtures, URLs, or notification defaults.

• The capability is independently reviewable and rollback-safe.

Validation

• Run draft timing and conflict, send idempotency, attachment lifecycle, background transfer, APNs token rotation, notification privacy, deep-link, termination, and physical-device tests.

• Run Swift build, XCTest, strict concurrency checks, generated-client diff, and the affected simulator and physical-device UI tests.

• Use sanitized fixtures and protected accounts only for final manual provider validation.

Dependencies

Post-1.0 work. Blocked until Mailflow 1.0.0 is released: https://github.com/Tutitoos/mailflow/milestone/9

Risks

Offline state, background execution, notification privacy, generated contracts, and device credentials can diverge from server truth. Use actors, Keychain, bounded caches, explicit conflict states, and real-device validation.

Out of scope

• Undo send, scheduling, signatures, templates, notification service extensions with mail content, and widgets.