fix: skins QA problems + flow change

[IMB11]

• Mojang is now treated as source of truth while the local DB is just saved skins/default cape state.
• Before replacing a Mojang-only skin, we save it locally so switching skins does not lose it.
• Saved skin PK is now texture_key + variant with cape_id becoming only metadata, which fixes duplicate skin rows.
• Other bug fixes + QOL - adding cache types to profile fetching
• Removed "default cape" concept
• Align with figma designs

[modrinth-bot]

Pull request changelog

App

Added

Changed

Deprecated

Removed

Fixed

Security

Website

Added

Changed

Deprecated

Removed

Fixed

Security

Hosting

Added

Changed

Deprecated

Removed

Fixed

Security

[modrinth-bot]

Frontend previews

Last deployed commit is 2a4c5c7e67c00e9ddfc3d0e0d466289d5c04ab46

Environment	URL
staging	https://git-2a4c5c7e-frontend-staging.modrinth.workers.dev
production	https://git-2a4c5c7e-frontend.modrinth.workers.dev
storybook	https://git-2a4c5c7e-storybook.modrinth.workers.dev