feat(media): add SD downloads, local playback and timed captions

[doodlewind]

Media playback currently depends on a companion socket. This adds a worker-owned SD library so apps can download a prepared media package and play, pause, seek and display timed captions without the companion.

The storage worker transfers acknowledged 32 KiB blocks, validates CRC32 and file readback, exports WebVTT, and commits a complete package. Local playback uses an IDR index and restores the active caption at seek. VirtualList exposes a long-press callback that suppresses release activation. The private 3DS host ABI advances to 11; existing launchers need replacement.

Consumer integration: pocket-stack/pocket-youtube#10.

Validation:

• All GitHub checks passed at 3b39f4d3.
• Native C storage worker tested with real sockets/files and a desktop thread shim: download, readback, reboot scan, delete, corruption, truncation, cancellation and storage failure.
• Media, 3DS profile/runtime/SOC and npm packaging checks passed; gesture and VirtualList checks: 46 passed.
• Pocket YouTube integration built .3dsx and .cia; real H.264 fixture and dual-screen journeys passed.
• Physical SD downloading, MVD playback, caption timing and touch acceptance remain pending a console runtime session. Software and FTP receipts do not establish those gates.