[MEDIA-014] RAW and JPEG pair awareness

[veryCrunchy]

Parent epic: #10
Related Photos epic: #14

User problem

RAW and JPEG captures that represent one photograph must not appear as unrelated duplicates, lose either original, or make one source impossible to open. A stacked item should remain one navigation page while still allowing the user to inspect and choose every retained source.

Goal

Preserve RAW/JPEG pairs as one logical media stack across upload, backup status, browsing, source selection, sharing, download, and restore without flattening or discarding either original.

Scope

• detect related RAW and JPEG files without relying only on a filename extension
• upload and verify every member independently while reporting one logical backup state
• show one gallery and timeline item for the pair
• retain the JPEG cover and RAW source as selectable members of the same viewer page
• keep previous and next navigation at one page per logical stack
• preserve independent originals, metadata, timestamps, filenames, receipts, and cache identities
• handle missing, unsupported, or temporarily unavailable members without hiding the accessible source
• keep stack identity account-scoped and deterministic across refresh, offline cache, move, download, and restore

Acceptance criteria

• RAW/JPEG pairs can upload together, share one visual stack, and retain independent originals and receipts
• selecting the RAW or JPEG source opens that exact member without creating duplicate previous or next pages
• moving away from a stack and returning selects a valid member deterministically
• partial upload, retry, conflict, missing companion, duplicate filename, and cross-account isolation have deterministic tests
• gallery, timeline, viewer, share, download, offline, and restore flows preserve the logical relationship
• Android emulator and desktop validation cover source selection and one-page-per-stack navigation