[Vela OTA] Sub-Issue 12: FlashPack Builder CLI tool

[JusterZhu]

Sub-Issue 12: FlashPack Builder CLI

Build a command-line tool for constructing, signing, verifying, and inspecting FlashPack (.fpk) bundles.

Commands

• \�uild\ — construct .fpk from payload with metadata
• \�erify\ — validate FlashPack structure
• \info\ — display detailed metadata
• \delta\ — generate binary delta via vela-delta
• \sign\ — sign with PEM key (future)

Design

Binary crate \�ela-builder\ in vela-core workspace.