feat(skills): enhance agent skills with additional tags and commands

- Added language_tags, library_tags, framework_tags, and domain_tags to agent skills.
- Introduced new commands: get_skill and get_guardrail for fetching specific skills and guardrails.
- Updated database schema and migration scripts to accommodate new fields.
- Enhanced skill listing functionality to support filtering by new tags.
- Improved error handling and response structures for skill-related operations.

schema/skills.dbml

@@ -5,6 +5,10 @@ Table agent_skills {
   description text [not null, default: '']
   content text [not null]
   tags "text[]" [not null, default: `'{}'`]
+  language_tags "text[]" [not null, default: `'{}'`]
+  library_tags "text[]" [not null, default: `'{}'`]
+  framework_tags "text[]" [not null, default: `'{}'`]
+  domain_tags "text[]" [not null, default: `'{}'`]
   created_at timestamptz [not null, default: `now()`]
   updated_at timestamptz [not null, default: `now()`]
 }