release: sync develop into main

[bitifirefly]

Summary

• Merge accumulated development work from develop into main.
• Includes backend hardening, multimodal handling improvements, provider/runtime fixes, and documentation cleanup.

Notable Areas

• Agent/runtime: status command, direct-processing envelope unification, session and cron fixes.
• Tools/providers: exec path guard improvements, MCP timeout/transport fixes, LiteLLM and gateway updates.
• Multimodal/data path: image block return in tool outputs, metadata cleanup for provider calls.
• Security/reliability: filesystem boundary checks, allowlist matching hardening, long-running client lifecycle fixes.
• Docs: legacy naming cleanup in skills/deployment docs.

Validation

• Changes have been continuously validated on develop through incremental test runs during each merge batch.
• This PR is for release-line convergence from develop to main.