Add MiniMax-H3 video generation to Camelid Desktop

[timtoole02]

Summary

• add an experimental MiniMax-H3 video lane backed by the checked H3-capable sd-cli
• add CLI pull, doctor, dry-run, and generate flows with license acknowledgement, SHA-256 verification, safe defaults, and a bounded asynchronous job API
• add Video Studio to the desktop UI with bundle selection, progress, cancellation, logs, and range-capable WebM playback
• support keeping the full 26.98 GB model bundle and outputs on removable storage while optionally bundling only sd-cli inside the app
• make the Windows desktop path reliable: inherit the resolved server model store, preserve case-insensitive external-drive layouts, hide backend console windows, and stage sd-cli.exe with its runtime DLLs
• bound removable-volume metadata scans and backend preflight so a slow or unapproved external drive cannot freeze the UI
• restore the native macOS title bar after the overlay drag region proved unreliable

Why

Camelid had no isolated video-generation path for MiniMax-H3 GGUF artifacts. The implementation keeps H3 separate from autoregressive chat inference, fails closed when artifacts or backend support are missing, and gives desktop users a practical external-drive workflow.

The native title-bar change fixes the observed macOS window that rendered correctly but could not be dragged.

The Windows follow-up removes reliance on Explorer's arbitrary process working directory and prevents sd-cli.exe preflight or generation from flashing a console window.

User impact

Users can install a selected MiniMax-H3 bundle, choose its external-drive folder from Video Studio, submit and cancel local video jobs, inspect backend logs, and play completed WebM output in the UI. No model weights, generated videos, or external-drive files are included in this PR.

Windows builders can stage a checked sd-cli.exe and its sibling runtime DLLs into the existing Tauri resource layout with scripts/stage-windows-h3-backend.ps1. The multi-gigabyte model bundle remains outside the installer.

Support remains explicitly experimental and uses the upstream MiniMax-H3 Community License.

Validation

• cargo test --lib minimax_h3::tests — 9 passed
• cargo test --lib api::video::tests — 5 passed
• cargo test --bin camelid video — 2 passed
• cargo test --manifest-path camelid-desktop/Cargo.toml — 20 passed
• npm --prefix frontend run build
• release macOS desktop bundle built, codesigned, installed, and launched on Apple M4
• full external bundle detected at 26,978,253,672 bytes with all four artifact sizes matching
• bundled and external sd-cli SHA-256 matched: 4471f542ae490d951da623b64c854e2055df59a254bd93ed88f8edfab4066c2d

Windows validation (2026-08-11):

• cargo test --lib minimax_h3::tests — 8 passed (the ninth test is Unix-only)
• cargo test --lib api::video::tests — 7 passed
• cargo test --bin camelid video — 2 passed
• cargo test --manifest-path camelid-desktop/Cargo.toml — 22 passed
• cargo clippy --lib -- -D warnings
• npm.cmd --prefix frontend run build
• scripts/stage-windows-h3-backend.ps1 smoke-tested with a renamed executable and sibling runtime DLL

Stack

This draft is intentionally based on codex/huggingface-model-catchup (PR #644) so this PR contains only the scoped H3/video diff. Rebase or retarget it to main after the parent lands.

Do not merge yet.

[timtoole02]

Superseded by #648, which contains only the generic desktop and model-storage reliability changes and is based directly on main. This stacked PR should not be merged.