Add unified OTA capability for edge_agent (SD + HTTP)

[jason-mao]

Background

This change introduces a unified OTA capability in edge_agent, covering both SD-card and HTTP update paths.

Changes

• Add new app_ota component for OTA orchestration.
• Integrate OTA boot flow in edge_agent startup.
• Support OTA from SD (/sdcard/firmware.bin) and HTTP manifest/firmware endpoints.
• Update project wiring (component deps, build/config, partition-related settings) required by OTA integration.
• Add component-level docs for OTA usage and configuration.

Validation

• SD OTA path: firmware discovery, version check, and update/skip behavior verified.
• HTTP OTA path: manifest/firmware fetch and version-based decision flow verified.
• Expected reject behavior confirmed when incoming version is not higher than current version.

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[laride]

sha=07313a60474fb820077f915cf3b6f9bbbe0fec70