Share skills between harnesses

[ea-rus]

Share skills as folder between harnesses (inside of single cowork instance)

Changes:

• store skills not in database but in folder (using Agentskills specs)
  • reuse code from anton for parsing storing skills (depends on Convert skill storage to Agentskills standard anton#186)
  • migrate existed skills at the start and mark that it is done using _skills_migrated
• sharing between harnesses:
  • create symlink for hermes (~/.cowork/skills -> ~/.cowork/hermes/skills)
  • set a cowork skills folder in anton settings as skills source

For back compatibility GUI column names are kept the same, current skills columns mapping:

GUI (cowork)	cowork-server	AgentSkill (anton)
label	label	name
name	display_name	metadata.display_name

Depend on mindsdb/anton#186

TODO later:

• skills table in database is not removed in this PR, should be removed in future migrations