feat: add vehicle, signature, and mobile scanner foundations

[Ewatomi5]

Summary

• add fleet vehicle registration types covering vehicle categories, capacity, and uploaded documents
• add a typed vehicle service for registration, retrieval, updates, deletion, multipart document uploads, and normalized API errors
• add reusable signature capture state with mouse and touch drawing, PNG export, clearing, empty-state checks, and listener cleanup
• add a mobile QR scanner hook with rear-camera constraints, one-frame-per-second decoding, permission states, iOS inline playback, and media-track cleanup

Validation

• 16 focused Jest tests passed
• changed-file ESLint passed
• changed-file TypeScript check passed
• git diff --check passed

Closes #819
Closes #820
Closes #823
Closes #827

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